Bioactive soft tissue implant and methods of manufacture and use thereof

ABSTRACT

A bioactive filamentary structure includes a sheath coated with a mixture of synthetic bone graft particles and a polymer solution forming a scaffold structure. In forming such a structure, synthetic bone graft particles and a polymer solution are applied around a filamentary structure. A polymer is precipitated from the polymer solution such that the synthetic bone graft particles and the polymer coat the filamentary structure and the polymer is adhered to the synthetic bone graft particles to retain the graft particles.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. patent application Ser. No. 15/584,620 filed May 2, 2017, now U.S. Pat. No. 10,729,548, which claims the benefit of the filing date of U.S. Provisional Patent Application No. 62/330,584 filed May 2, 2016, and is a continuation-in-part of U.S. patent application Ser. No. 15/234,239 filed Aug. 11, 2016, published as U.S. Patent Application Publication No. 2017/0043052 A1, which claims the benefit of the filing date of U.S. Provisional Patent Application No. 62/204,119, filed Aug. 12, 2015, the disclosures of all of which are hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to bone suture anchors, and more particularly, to bioactive suture anchors and the preparation thereof.

BACKGROUND OF THE INVENTION

Surgical sutures and suture anchors are used to close or hold together various types of soft tissue, including but not limited to skin, blood vessels, and internal organ tissue. In many instances, such sutures as well as all-suture suture anchors are made of biocompatible materials such as but not limited to non-absorbable materials such as cellulose (cotton, linen), protein (silk), processed collagen, nylon, polyester, polypropylene, aromatic polyamides (“aramid”), polytetraflourethylene, steel, copper, silver, aluminum, various alloys and the like, including many proprietary polymers and composites, to bioabsorbable (or biodegradable or bioerodible) synthetic materials, such as polymers and copolymers of glycolic and lactic acid. In some instances, such sutures have been coated with materials that provide additional benefits including antimicrobial, tribological properties, further biocompatible properties, and as well as materials that have properties to promote tissue growth and repair, including biodegradable matrices of growth factor molecules.

These suture and coating combinations often do not satisfy their desired efficacy as coatings are either removed during insertion of coated sutures due to abrasive contact with neighboring tissue or are rapidly degraded and diffused into the body before the coating can exert significant beneficial effects at the target site. Supplying high concentrations of bioactive material to the target site is not an effective solution as such concentrations may negate the benefits and indeed could be harmful, and further are relatively costly.

Attempting to address these issues, complex suture designs have utilized a multifilament biodegradable porous core surrounded by a biodegradable braided or woven sheath in which a concentration of living cells are retained within interstices disposed between the filaments of the core. In such designs, the sheath inhibits migration of the living cells from the porous core.

These designs require a concentration of bioactive material such as living cells and therapeutic agents throughout the cores and thus cannot be used with standard sutures as cores. Accordingly, other methods of preparation are needed to provide biocompatibility and tissue growth promotion benefits to surgical sutures and anchors made of suture material.

Bone graft materials are used in many applications within the orthopedic and/or other medical fields, such as to cause fusion of adjacent bone parts to repair a fracture, to fuse a joint(s) and alleviate pain at the joint(s), and/or more securely attach an implant or other device to bone. Bone graft materials have numerous indications within the orthopedic field, which rely on the ability of the material to facilitate natural bone growth at the repair site (e.g., for regenerating and/or forming additional bone at the site).

There has been a continuing need for improved bone graft materials. For example, autograft devices, which are processed from a patient's own bone, have the ideal properties and radiopacity. However, the use of autogenous bone exposes the patient to a second surgery, pain, and morbidity at the donor site. Allograft devices, which are processed from donor bone, also carry the risk of disease transmission. These devices are restricted in terms of variations on shape and size and have sub-optimal strength properties that decrease after implantation. The quality of the allograft devices varies because the devices are natural. Also, since companies that provide allograft implants obtain their supply from donor tissue banks, there tend to be limitations on supply.

In recent years, synthetic materials have become a viable alternative to autograft and allograft devices. Most synthetic materials share numerous advantages over allografts, autografts and demineralized bone matrix (“DBM”), such as unlimited supply, elimination of disease transmission, elimination of second surgery, and the ability to be shaped into various shapes and sizes. Many synthetic bone grafts include materials that closely mimic mammalian bone, such as compositions containing calcium phosphates. Exemplary calcium phosphate compositions contain type-B carbonated hydroxyapatite [Ca₅(PO₄)_(3x)(CO₃)x(OH)], which is the principal mineral phase found in the mammalian body. Calcium phosphate ceramics have been fabricated and implanted in mammals in various forms including, but not limited to, shaped bodies and cements. Different stoichiometric compositions such as hydroxyapatite (“HAp”), tricalcium phosphate (“TCP”), tetracalcium phosphate (“TTCP”), and other calcium phosphate salts and minerals, have all been employed to match the adaptability, biocompatibility, structure, and strength of natural bone. The role of pore size and porosity profile in promoting revascularization, healing, and remodeling of bone have been recognized as a critical property for bone grafting materials. The preparation of exemplary porous calcium phosphate materials that closely resemble bone have been disclosed, for instance, in U.S. Pat. Nos. 6,383,519; 6,521,246 and 6,991,803, which are incorporated herein by reference in their entirety.

The Vitoss® line of synthetic bone graft products (manufactured by Stryker Orthobiologics, Malvern, Pa.) includes β-TCP (i.e., beta tri-calcium phosphate), collagen, and/or bioactive glass.

Scaffolds may be used to support bone graft materials. Among the most commonly used scaffolds in medical devices are mammalian-derived collagens (A. Oyran et al., J. Orthop. Surg. Res. 2014 Mar. 17; 9(1):18).

Synthetic scaffolds using biocompatible polymers, such as PCL are also available and may be formed by, or using, molding, solvent casting, particulate leaching, solvent evaporation, electrospun fibers or meshes thereof, and 3-D printed constructs. (see M. A. Woodruff and D. W. Hutmacher, The return of a forgotten polymer: Polycaprolactone in the 21^(st) century. Progress in Polymer Science, p. 1-102, Elsevier Press (2010)) Highly ordered, crystalline constructs having properties akin to those of solvent casted scaffolds can also be formed. (A. G. A. Coombes et al., Biomaterials 25 (2004) 315-325). Unfortunately, those synthetic scaffolds lack the foam-like consistency, and are of a higher density and stiffer, and lack several desirable properties, such as porosity to soak up and retain biological fluids, moldability and compressibility to fit into a hole or defect in bone.

Despite advances in synthetic materials for bone graft applications, there remains a need in the art for further improvements, such as materials having tunable properties, lacking animal tissue-derived materials, and which can be manufactured without complex methods.

BRIEF SUMMARY OF THE INVENTION

In accordance with an aspect, a bioactive filamentary structure includes a sheath coated with a mixture of synthetic bone graft particles and a polymer forming a scaffold structure. In some arrangements, the synthetic bone graft particles may include bioactive (BA) glass and the polymer may include polycaprolactone (PCL). In some arrangements, a layer of the synthetic bone graft particles may be generally above a layer of the polymer. In some other arrangements, a layer of the synthetic bone graft particles may be generally below the layer of the polymer. In some such arrangements, at least some of the synthetic bone graft particles may extend and be exposed through the layer of the polymer to promote bone ingrowth upon insertion of the bioactive filamentary structure into a bone hole at a surgical repair, i.e., treatment, site.

In some arrangements, the bioactive filamentary structure may define a lumen through which a filament, which may be a suture or other thread-like material, may be passed. In some such arrangements, the bioactive filamentary structure may be constructed of synthetic material (e.g., PLGA, UHMWPE, or the like) or of organic material (silk, animal tendon, or the like).

In accordance with another aspect, a bioactive filamentary structure may be formed. Synthetic bone graft particles may be applied around a filamentary structure. A polymer solution may be applied around the filamentary structure. A polymer may be precipitated from the polymer solution such that the synthetic bone graft particles and the polymer may coat the filamentary structure.

In some arrangements, the synthetic bone graft particles may be applied around the filamentary structure by placing the filamentary structure into a container of synthetic bone graft particles and subsequently removing the filamentary structure from the container. In some such arrangements, the container of the synthetic bone graft particles may be shaken during placement of the filamentary structure into the container. In some such arrangements of applying the synthetic bone graft particles around the filamentary structure, the filamentary structure may be disposed on an inserter, which may be used for later placement of the filamentary structure, for handling of the filamentary structure during placement of the filamentary structure into the container of the synthetic bone graft particles.

In some arrangements, the polymer solution may be applied around the filamentary structure prior to applying the synthetic bone graft particles around the filamentary structure. In some such arrangements, the polymer solution may be applied directly to the filamentary structure. In some such arrangements of applying the polymer solution around the filamentary structure, the polymer solution may be sprayed around the filamentary structure. In other arrangements, the synthetic bone graft particles may be applied directly to the filamentary structure prior to applying the polymer solution around the filamentary structure.

In some arrangements, the synthetic bone graft particles used in forming the bioactive filamentary structure may include either of or both a calcium phosphate and a bioactive additive. In some arrangements of the synthetic bone graft particles, the bioactive additive may be but is not limited to being bioactive glass, bone chips, demineralized bone chips or powder, living cells, lyophilized bone marrow, collagen, other bioactive proteins or growth factors, biologics, peptides, glycosaminoglycans, anti-inflammatory compounds, antibiotics, anti-microbial elements, and mixtures of the foregoing. In some arrangements of the synthetic bone graft particles, the calcium phosphate may be but is not limited to being tetra-calcium phosphate, di-calcium phosphate, dicalcium phosphate dihydrous, dicalcium phosphate anhydrous, tri-calcium phosphate, mono-calcium phosphate, β-tricalcium phosphate, α tricalcium phosphate, oxypatite, hydroxypatite, and mixtures of any of the foregoing.

In some arrangements, the polymer precipitated from the polymer solution used in forming the bioactive filamentary structure may be but is not limited to being polycaprolactones (PCL), polyglycolides (PGA), polylactic acids (PLA), polyethylene, polypropylene, polystyrene, poly(D,L-lactic-co-glycolide) (PLGA), polyglycolic acid (PGA), poly-L-Lactic acid (PL-LA), polysulfones, polyolefins, polyvinyl alcohol (PVA), polyalkenoics, polyacrylic acids (PAA), polyesters, lower alkyl cellulose ethers, methylcellulose, sodium carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethylcellulose, carboxymethyl cellulose, and mixtures of any of the foregoing.

In some arrangements, the polymer solution used in forming the bioactive filamentary structure may include at least one solvent. The solvent may be but is not limited to being glacial acetic acid (GAA), acetic acid, anisole, chloroform, methylene chloride, acetylchloride, 2,2,2 trifluoroethanol, trifluoroacetic acid, 1,2-Dochloroethane, and mixtures of any of the foregoing. In preferred arrangements, the polymer solution may contain polycaprolactone (PCL) and glacial acetic acid (GAA).

In some arrangements of forming the bioactive filamentary structure, the polymer may be precipitated from the polymer solution by applying to the polymer solution a precipitating agent. The precipitating agent may be but is not limited to being sodium phosphate buffer, water, ethanol, 1-propanol, isopropyl ether, 2-butanol, hexane, and mixtures of any of the foregoing.

In some arrangements of forming the bioactive filamentary structure, the polymer may be precipitated from the polymer solution by immersing the polymer solution in a precipitating agent after applying both the synthetic bone graft particles and the polymer solution around the filamentary structure.

In some arrangements of forming the bioactive filamentary structure, the polymer may be precipitated from the polymer solution by applying a first buffer to the polymer solution after the polymer solution is applied around the filamentary structure. In this manner, the polymer solution may be partially neutralized.

In some arrangements of forming the bioactive filamentary structure, a second buffer may be applied to the polymer solution after the first buffer is applied around the filamentary structure to further dilute the polymer solution. In some such arrangements, the first and the second buffers may be sodium phosphate buffers.

In some arrangements of forming the bioactive filamentary structure, the coated filamentary structure may be dried at least after the application of the first buffer to the polymer solution. In some such arrangements, the coated filamentary structure may be dried after the application of the second buffer to the polymer solution.

In some arrangements of forming the bioactive filamentary structure, the coated filamentary structure may be placed into and may be sealed within sterile packaging, preferably after the coated filamentary structure is dried.

In some arrangements, the coated filamentary structure may be disposed on an inserter used for placing the coated filamentary structure into a treatment site. In some such arrangements, the coated filamentary structure disposed on the inserter may be placed into and may be sealed within sterile packaging, preferably after the coated filamentary structure is dried.

In accordance with another aspect, a bioactive filamentary structure may be formed. In this aspect, synthetic bone graft particles may be mixed with a polymer solution to form a scaffold mixture. The scaffold mixture may be applied around a filamentary structure. A polymer may be precipitated from the polymer solution such that the synthetic bone graft particles and the polymer coat the filamentary structure.

In accordance with another aspect, a bioactive filamentary structure may include a filamentary structure, synthetic bone graft particles, and a polymer. The synthetic bone graft particles may coat the filamentary structure. The polymer may partially coat the synthetic bone graft particles such that at least some of the bone graft particles may be at least partially exposed through the polymer coating. In some arrangements, the filamentary structure may be an all-suture suture anchor. In some arrangements, the bone graft particles exposed through the polymer coating may extending from the filamentary structure beyond the polymer coating.

Scaffolds and methods of forming the same are disclosed herein. In some embodiments, a method of forming a scaffold includes dissolving a polymer in a solvent to form a polymer solution; adding a precipitating agent to the polymer solution; precipitating and expanding the polymer from the polymer solution to form a scaffold; and removing the solvent from the scaffold.

In some embodiments, a method of forming a scaffold includes dissolving a polymer in a solvent to form a polymer solution; adding a precipitating agent to the polymer solution; precipitating the polymer from the polymer solution to form a scaffold comprising an amorphous polymer matrix; and removing the solvent from the scaffold.

In some embodiments, a method of forming a scaffold includes dissolving a polymer in a solvent to form a polymer solution; adding a precipitating agent to the polymer solution; precipitating the polymer from the polymer solution to form a scaffold, wherein the time to form the scaffold by precipitation of the polymer ranges from about 1 minutes to about 1 hour; and removing the solvent from the scaffold.

In some embodiments, a method of forming a scaffold includes dissolving a polymer in a solvent to form a polymer solution; adding a precipitating agent to the polymer solution; precipitating the polymer from the polymer solution to form a scaffold, wherein a weight ratio of the precipitating agent to the polymer solution ranges from about 0.05:1 to about 3.5:1; and removing the solvent from the scaffold.

In some embodiments, a scaffold comprises an amorphous polymer matrix having a density ranging from about 0.025 g/cm³ to about 0.063 g/cm³.

In some embodiments, a scaffold comprises an amorphous polymer matrix having at least one of calcium phosphate or bioactive material embedded therein.

In some embodiments, prior to adding the precipitating agent, the method further comprises adding at least one of calcium phosphate or a bioactive additive to the polymer solution to form a mixture, wherein after precipitating the polymer, the scaffold formed includes the at least one of calcium phosphate or bioactive additive embedded therein.

In some embodiments, an amount of calcium phosphate ranges from about 15 weight % to about 40 weight %, based on the total weight of the mixture.

In some embodiments, the method further comprises, prior to adding the at least one of calcium phosphate or bioactive additive to the polymer solution, soaking the at least one of calcium phosphate or bioactive material with the precipitating agent to form a precipitating agent-soaked additive; and freezing the precipitating agent-soaked additive.

In some embodiments, the method further comprises, prior to precipitating the polymer, freezing the mixture.

In some embodiments, the precipitating agent is selected from the group consisting of water, ethanol, 1-propanol, isopropyl ether, 2-butanol, hexane, and mixtures thereof.

In some embodiments, the method further comprises adding the precipitating agent drop wise.

In some embodiments, the method further comprises adding the precipitating agent by spraying or misting the precipitating agent onto a surface of the polymer solution or the mixture of polymer solution and at least one of calcium phosphate or bioactive additive.

In some embodiments, the method further comprises adding the precipitating agent by flowing or pouring the precipitation agent onto the surface of the polymer solution or the mixture of polymer solution and at least one of calcium phosphate or bioactive additive.

In some embodiments, the polymer solution or the mixture of polymer solution and at least one of calcium phosphate or bioactive additive is submerged in the precipitating agent.

In some embodiments, the method further comprises, prior to precipitating the polymer, placing the mixture into a mold.

In some embodiments, the method further comprises, prior to precipitating the polymer, depositing the mixture on a substrate.

In some embodiments, the substrate is selected from the group consisting of a mesh or screen, a porous polymer substrate, a bone suture anchor, a porous metal implant, living tissue, decellularized tissue, and mixtures thereof.

In some embodiments, prior to precipitating the polymer, the method further comprises soaking the substrate with the precipitating agent.

In some embodiments, the polymer is at least one selected from the group consisting of polycaprolactones (PCL), polyglycolides (PGA), polylactic acids (PLA), polyethylene, polypropylene, polystyrene, poly(D,L-lactic-co-glycolide) (PLGA), polyglycolic acid (PGA), poly-L-Lactic acid (PL-LA), polysulfones, polyolefins, polyvinyl alcohol (PVA), polyalkenoics, polyacrylic acids (PAA), polyesters, lower alkyl cellulose ethers, methylcellulose, sodium carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethylcellulose, carboxymethyl cellulose, and mixtures thereof.

In some embodiments, the calcium phosphate is at least one selected from the group consisting of tetra-calcium phosphate, di-calcium phosphate, dicalcium phosphate dihydrous, dicalcium phosphate anhydrous, tri-calcium phosphate, mono-calcium phosphate, β-tricalcium phosphate, α-tricalcium phosphate, oxypatite, hydroxypatite, and mixtures thereof.

In some embodiments, the calcium phosphate is porous.

In some embodiments, the solvent is at least one selected from the group consisting of glacial acetic acid (GAA), acetic acid, anisole, chloroform, methylene chloride, acetylchloride, 2,2,2 trifluoroethanol, trifluoroacetic acid, 1,2-Dochloroethane, and mixtures thereof.

In some embodiments, the bioactive additive is at least one selected from the group consisting of bioactive glass, bone chips, demineralized bone chips or powder, living cells, lyophilized bone marrow, collagen, other bioactive proteins or growth factors, biologics, peptides, glycosaminoglycans, anti-inflammatory compounds, antibiotics, anti-microbial elements, and mixtures thereof.

In some embodiments, the polymer is polycaprolactone (PCL) and wherein the solvent is glacial acetic acid (GAA).

In some embodiments, the polymer is polycaprolactone (PCL) and wherein the solvent is anisole.

In some embodiments, an amount of polymer dissolved in the polymer solution ranges from about 4 wt % to about 15 wt %, relative to the total weight of the polymer solution.

In some embodiments, the calcium phosphate is β-tricalcium phosphate (β-TCP).

In some embodiments, an amount of calcium phosphate ranges from about 20 wt % to about 30 wt %, relative to the total weight of the mixture.

In some embodiments, the polymer has a molecular weight ranging from about 3,000 g/mol to about 150,000 g/mol.

In some embodiments, the time to form the scaffold by precipitation of the polymer ranges from about 1 minute to about 1 hour.

In some embodiments, the time to form the scaffold by precipitation ranges from about 5 minutes to about 30 minutes.

In some embodiments, a weight ratio of the precipitating agent to the polymer solution ranges from about 0.05:1 to about 3.5:1.

In some embodiments, a weight ratio of the precipitating agent to the polymer solution ranges from about 0.5:1 to about 3:1.

In some embodiments, an amount of calcium phosphate ranges from about 15 weight % to about 40 weight %, based on the total weight of the mixture.

In some embodiments, removal of the solvent further includes removal of the precipitating agent.

In some embodiments, a time for removal of the solvent and/or the precipitating agent ranges from about 5 minutes to about 3 hours.

In some embodiments, a time for removal of the solvent and/or the precipitating agent ranges from about 5 minutes to about 1 hour.

In some embodiments, a time for removal of the solvent and/or the precipitating agent ranges from about 5 minutes to about 30 minutes.

In some embodiments, a time for removal of the solvent and/or the precipitating agent ranges from about 20 minutes to about 30 minutes.

In some embodiments, the scaffold comprises an amorphous polymer matrix.

In some embodiments, the scaffold comprises at least one of calcium phosphate or a bioactive additive embedded in the amorphous polymer matrix.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description and accompanying drawings in which:

FIG. 1 is a perspective view of a sheath and filament combination of the prior art;

FIG. 2 is a perspective view of a sheath and filament combination in accordance with an embodiment;

FIGS. 3A and 3B are portions of a process flow diagram for preparing the sheath and filament combination shown in FIG. 2;

FIGS. 4A and 4B are perspective views of the sheath and filament combination shown in FIG. 2 in pre-deployment and deployed states;

FIGS. 5A and 5B are plan views of respective portions of sheaths exposed to simulated body fluid in accordance with other embodiments;

FIG. 6 is a perspective view of a sheath and filament combination in accordance with another embodiment; and

FIG. 7 is a perspective view of a portion of a process flow diagram for preparing the sheath and filament combination shown in FIG. 6.

FIGS. 8A-8D depict scaffolds made using a range of concentrations for a polymer solution in accordance with some embodiments of the present invention.

FIGS. 9A-9F depict scaffolds made using a range of amounts of a polymer solution in accordance with some embodiments of the present invention.

FIG. 10 depicts a scaffold in accordance with one embodiment of the present invention.

FIG. 11 depicts a scaffold in accordance with another embodiment of the present invention.

FIGS. 12A-12D depict scaffolds in accordance with some embodiments of the present invention.

FIG. 13A depicts a substrate in accordance with some embodiments of the present invention.

FIG. 13B depicts a scaffold including the substrate of FIG. 13A in accordance with some embodiments of the present invention.

FIG. 14A depicts a substrate in accordance with some embodiments of the present invention.

FIG. 14B depicts a scaffold including the substrate of FIG. 14A in accordance with some embodiments of the present invention.

FIG. 14C depicts a scaffold including the substrate of FIG. 14A in accordance with some embodiments of the present invention.

FIG. 14D depicts a scaffold including the substrate of FIG. 14A in accordance with some embodiments of the present invention.

FIG. 15 depicts high magnification image of the scaffold depicted in FIG. 14B.

FIG. 16A depicts a scanning electron microscopy (SEM) image of the scaffold of FIG. 14C.

FIG. 16B depicts an EDAX (energy dispersive x-ray) chemical map of the SEM image of FIG. 16A.

FIG. 16C depicts EDAX data of the scaffold of FIG. 14C.

FIGS. 17A-17B depict SEM images of a scaffold in accordance with some embodiments of the present invention.

FIG. 18 depicts EDAX data from a region of the scaffold depicted in FIG. 17A.

FIG. 19 depicts an SEM image of a scaffold in accordance with some embodiments of the present invention.

FIG. 20A depicts EDAX data from regions of a scaffold in accordance with some embodiments of the present invention.

FIG. 20B depicts EDAX data from regions of the scaffold depicted in FIG. 19 in accordance with some embodiments of the present invention.

FIG. 21A depicts scaffolds formed using different amounts of precipitating agent in accordance with some embodiments of the present invention.

FIG. 21B depicts the thickness variation of the scaffolds depicted in FIG. 21A as function of the amount of precipitating agent added in accordance with some embodiments of the present invention.

FIG. 22 depicts scaffolds formed using different orders of processing steps in accordance with some embodiments of the present invention.

DETAILED DESCRIPTION

As used herein, the term “filament” and like terms are inclusive of single or multiple strands, threads, fibers, strings, wires or sutures in which such terms preferably refer to a suture or other thread-like material, and in particular a braided suture, having a hollow core along at least a portion of its length. A filament may be constructed from homogenous or heterogeneous materials such as, but not limited to, polyester, polyethylene (including ultra-high molecular weight polyethylene (UHMWPE)), polytetrafluorethylene (including expanded polytetrafluorethylene), nylon, polypropylene, aramids (such as Kevlar-based materials), polydioxanone, polygycolic acid, liquid crystal polymer (LCP), organic material (silk, animal tendon, or the like), metallic wire, or any combination of these materials.

Referring now to the drawings, as shown in FIG. 1, sheath and filament combination 10 known in the art forms an all-suture suture anchor that includes first filament 15A and second filament 15B, which in some arrangements may be a monofilament while in other arrangements may be a braided suture as shown, and sheath 20 having an inner lumen defined by inner surface 27 of the sheath through which the filament is inserted. Preferably, each of sheath 20 and the filaments 15A, 15B are composed of suture, and specifically a blend of UHMWPE and polyester. Sheath 20, which may be but is not limited to being a sheath of an all-suture suture anchor for use as part of the ICONIX® All Suture Anchor System, includes openings 25 along its length that expose filaments 15A, 15B and allow the sheath to fold upon itself and to compress when opposing portions of the filament are pulled in a direction away from the sheath while the sheath is held, such as by a patient's bone or other tissue, at its ends. This deformation of the sheath drastically changes an aspect ratio of the sheath to provide a resistance to pullout when the suture is inserted into a prepared bone hole (see FIG. 4B for an example of this deformation being applied to prepared sheath 120 prepared in accordance with an embodiment of the present invention), as described in U.S. Pat. No. 9,445,803 to Marchand et al. (“the '803 Patent”), which is hereby incorporated by reference in its entirety herein.

As shown in FIG. 2, sheath and filament combination 110 includes first filament 15A, second filament 15B, and prepared sheath 120 having an inner lumen through which the filament is inserted. Prepared sheath 120 is generally formed by applying synthetic bone graft particles, which may be but are not limited to being bioactive (BA) glass or calcium phosphate particles, onto and within sheath 20 and then coating the synthetic bone graft particles with a polymer coating layer, which may be but is not limited to being a layer of polycaprolactone (PCL). The PCL acts as a barrier or otherwise secures the synthetic bone graft particles to prevent migration and rapid degradation and diffusion of the bone graft particles upon insertion of sheath and filament combination 110 into a treatment site.

Referring now to FIGS. 3A and 3B, in step 130, polymer solution 135 containing the polymer coating and a solvent in which the polymer coating may be soluble, which preferably may be acetic acid (AA) and more preferably may be glacial acetic acid (GAA), may be prepared by mixing the polymer coating in the solvent at an appropriate temperature for an appropriate time. In preferred arrangements, the polymer may be fully dissolved in the solvent. In one example, to form polymer solution 135, the mixture of the polymer and the solvent preferably may be placed on a heated plate, such as but not limited to the plate of an orbital shaker, set at a temperature in the range of approximately 30° C. to-approximately 55° C. for a time preferably less than 24 hours, or otherwise up until a time the polymer fully dissolves.

Once prepared, the molecular weight (MW) of the polymer coating may be but is not limited to being in the range of 33-117 kilodaltons (kDa). In general, greater MWs of the polymer coating will lead to greater bioactivity at a treatment site but will cause slower resorbability. However, bioactivity may vary with other variables such as but not limited to any of the amount, size, and surface area of the synthetic bone graft particles, coating thickness and porosity. In preferred arrangements, the concentration of polymer solution 135 may be in the range of about 5% to about 16% mass per unit volume, and preferably approximately 5%. The viscosity of polymer solution 135 may be desirably in the range of approximately 1 to approximately 30 centipoise (cP), and preferably about 20 cP. Within this viscosity range, polymer solution 135 may have sufficient flowability for application to sheath 20 while at the same time have sufficient adhesion characteristics to inhibit sliding of the solution off of the sheath after application. Alterations in concentration and molecular weight of polymer solution 135 may have an effect on droplet size, spray pattern, and the characteristics of the polymer coating after being applied to sheath 20.

In parallel with the preparation of polymer solution 135, sheath 20 is coated with synthetic bone graft particles, which may be but are not limited to being BA glass particles, at step 140. In some arrangements, sheath 20 may be held horizontally (i.e., parallel to the floor), such as by an operator or a robotic arm, and dipped into a container containing the bone graft particles. In such arrangements, openings 25 of sheath 20 may be oriented vertically upward (i.e., face away from the floor) during dipping of the sheath into the container such that the synthetic bone graft particles contact and enter only or at least mainly outer surface 26 (as illustrated in FIG. 1) of the sheath. In alternative arrangements, sheath 20 may be held in any other orientation, including vertically in which when the sheath is dipped into the container of the synthetic bone graft particles, such particles may coat at least a portion of inner surface 27 (identified in FIG. 1) of the sheath and may be held on the anchor by ionic forces, van der Waals' forces and physical entrapment between bone graft particles. Such interactions may be generated by static electricity caused by friction between the bone graft particles and the sheath during the dipping of the sheath. In some arrangements, the bone graft particles may be held mechanically by being placed in the interstices of the fibers of the sheath. In some alternative arrangements, a resistive mask (not shown), which may be but is not limited to being a tape, film, or other covering, may be applied over central openings 25 and end openings 29 of sheath 20 to prevent or at least inhibit the intrusion of synthetic bone graft particles into the inner lumen of the sheath defined by inner surface 27 of the sheath. In some arrangements, the resistive mask may prevent friction between first filament 15A and second filament 15B.

In preferred arrangements, sheath 20 may be dipped into the synthetic bone graft particles while surrounding filaments 15A, 15B as part of sheath and filament combination 10, while in other arrangements, sheath 20 may be separated from either or both of filaments 15A, 15B during the graft coating process. In arrangements in which sheath 20 is oriented with either of or both central openings 25 and end openings 29 exposed to the synthetic bone graft particles, at least a portion of either of filaments 15A, 15B may be coated with the synthetic bone graft particles along with sheath 20. To avoid coating either or both of filaments 15A, 15B or allowing synthetic bone graft particles to be incorporated between either of the filaments and the interior of sheath 20, a resistive mask (not shown) may be applied to the sheath over openings 25 during application of the synthetic bone graft particles onto the sheath. Reducing these particles in these areas may avoid introducing additional friction when sliding filaments 15A, 15B through sheath 20 after insertion of sheath and filament combination 10 into a prepared bone hole at a treatment site.

As shown in FIG. 3A, at step 139 prior to step 140, sheath and filament combination 10 may be placed onto an inserter (not shown), such as the inserter described in the '803 Patent or the inserter described in either of U.S. Pat. No. 8,821,494 B2 to Pilgeram and U.S. Patent Application Publication No. 2014/0039552 A1 to Pilgeram, the disclosures of each of which are hereby incorporated by reference herein. In this manner, the inserter may be held by the respective operator or robotic arm during placement of sheath 20, or in some arrangements sheath and filament combination 10, into the container of synthetic bone graft particles. Placing sheath 20 onto the inserter prior to loading with synthetic bone graft particles avoids any loss of the particles that may otherwise occur during such placement of the sheath. The particle size of the synthetic bone graft particles applied to sheath 20 is preferably in the range from about 32 μm to about 90 μm. Larger or smaller particles sizes are possible in which smaller particle sizes drive more bioactivity at a treatment site but may be resorbed too quickly for certain applications.

In some arrangements, the container of synthetic bone graft particles may be in the form of a bowl or cup, such as but not limited to a glass, plastic, or metal bowl. In some arrangements, either of or both the container and sheath 20 (and in some instances, the inserter and filament 15 as described previously herein) may be vibrated to prevent or inhibit agglomeration of the particles and to achieve an appropriate graft coating mass for a particular anchor size. In some arrangements, the container may be rotated, i.e., spun, and may be translated along with being vibrated. Vibration, translation, and rotation of the container allows the synthetic bone graft particles to uniformly, thoroughly, and continuously contact the outer surface of sheath 20. In this manner, the bone graft particles may coat sheath 20 and become wedged between fibers forming the sheath. The frequency and amplitude of either of or both the vibration and rotation may be altered by changing a corresponding voltage setting on a vibration fixture, which may be but is not limited to being a vibration table. These settings along with the time of vibration affect the mass of the synthetic bone graft particles applied to sheath 20. In this manner, the synthetic bone graft particles may be embedded between the fibers of sheath 20, and preferably agglomerates at pics of the fibers of the anchor. Sheath 20 may be tensioned and compressed along an axis, e.g., its longitudinal axis, to open the fibers of the sheath. In this manner, the synthetic bone graft particles may be set in between the fibers. Alternatively, sheath 20 may any of be vibrated, translated, and rotated relative to the container in order to coat the sheath with the synthetic bone graft particles. In some arrangements, after graft particles are applied to sheath 20, the sheath (along with filament 15 and the inserter if attached to the sheath) may be shaken to remove loose particles.

With reference to step 150 shown in FIG. 3A, graft-coated sheath 20 may be coated with polymer solution 135. Polymer solution 135 may coat, in one example, at least 30% of the outer surface of graft-coated sheath 20, in another example, at least 70% of the outer surface of graft-coated sheath, and, in still another example, at least 90% of the outer surface of graft-coated sheath, although in some arrangements, the polymer solution may coat less than 30% of the outer surface of the graft-coated sheath. In the example shown, polymer solution 135 may be sprayed, for example in the form of a mist, from a nozzle (not shown) onto some, or preferably all exposed areas, of graft-coated sheath 20. In some arrangements, the sprayer may be mechanical sprayer, in which the flow rate provided by the sprayer may be altered by increasing or decreasing the restriction within the nozzle of the sprayer. In other arrangements, the sprayer may be part of an ultrasonic spray system, e.g., the Sono-tek ExactaCoat SC ultrasonic spraying system, which includes an ultrasonic spray nozzle used in conjunction with an air stream directed to the nozzle and controlled with a gantry system, which may be operated by server motors, or other motion control system. In such arrangements, the flow rate of the spray as it exits the nozzle may be altered as desired by adjusting the voltage to piezoelectric transducers to create vibrations against and to cause the atomization of polymer solution 135 as it flows.

The flow rate of the spray, the local air pressure around the spray, the distance of the exit of the nozzle from graft-coated sheath 20 (or uncoated sheath 20 in other embodiments such as in the formation of prepared sheath 220 described further herein), the speed of the exit of the nozzle itself relative to the sheath, and the number of passes over an area or areas of the sheath all affect the thickness of polymer solution 135 applied to the graft-coated (or uncoated) sheath. Preferably, polymer solution 135 should not be too thin when applied to graft-coated (or uncoated) sheath 20 such that the solution does not sufficiently adhere to the respective coated (or uncoated) sheath. Conversely, polymer solution 135 should not be too thick such that either of or both sheath and filament combination 110 is too stiff and prepared sheath 120 (or other prepared sheath, such as prepared sheath 220) defines a maximum outer perimeter that is greater than an inner perimeter of a prepared bone hole into which the sheath is to be inserted and thus is susceptible to removal of the applied synthetic bone graft particles during such insertion.

Referring now to FIG. 3B, during step 160, polymer solution 135 coating sheath 20 is exposed to a precipitating agent, which may be but is not limited to being a sodium phosphate buffer composed of sodium monobasic and sodium dibasic in water (Na₂HPO₄ and NaH₂PO₄) or other neutral pH solution, which causes precipitation of the polymer coating from polymer solution 135 such that the polymer coating may coat the bone graft particles of prepared sheath 20 in order to retain the particles and prevent their premature degradation when prepared sheath 120 is inserted into a treatment site. In preferred arrangements, sheath 20 coated with solution 135, which in more preferred arrangements may be disposed on an inserter as discussed previously herein, is dipped into a reservoir containing the precipitating agent. In some alternative arrangements, the precipitating agent may be sprayed onto sheath 20 coated with polymer solution 135. Under certain of the conditions of the nozzle listed above with respect to the thickness of polymer solution 135, a stream, i.e., a fluid jet, of 10 mL to 20 mL of the buffer solution may be rapidly applied for less than approximately 30 seconds to sheath 20 prepared with polymer solution 135, again which in more preferred arrangements may be disposed on an inserter as discussed previously herein. In any of these arrangements, sheath 20 when coated with polymer solution 135 preferably is soaked or otherwise saturated with the precipitating agent immediately after application of polymer solution 135 in order to more evenly distribute the polymer solution and to reduce the exposure of the polymer solution, the synthetic bone graft particles when such particles are coating sheath 20, and the sheath itself to acidic conditions.

During step 170 and following precipitation step 160, sheath 20 coated with the polymer coating and remaining polymer solution 135 is washed, such as by but not limited to being by either of or both a sodium phosphate buffer and deionized (DI) water (“wash solution”). In this manner, residual salts that have formed, which may be acetate and phosphate salts from the GAA (or other form of AA) solvent used in polymer solution 135 and the sodium phosphate buffer used at step 160, are reduced to a physiologically acceptable range. In preferred arrangements, sheath 20 coated with the polymer coating and remaining polymer solution is washed in a bath containing the wash solution. The combination of precipitation step 160 and washing step 170 under proper conditions should yield a residual amount of the GAA (or other form of AA) solvent of preferably less than approximately 0.040 molar (M). Use of the buffer as or in the washing solution neutralizes the pH of the coating on sheath 20 more quickly during processing than water alone and thus prevents unnecessary erosion of the synthetic bone graft particles otherwise caused by the GAA (or other form of AA) solvent.

As further shown in FIG. 3B, during step 180, sheath 20 coated with the precipitated polymer coating covering the applied synthetic bone graft particles is subjected to drying to form prepared sheath 120 and to remove any residual GAA (or other form of AA). In this manner, degradation of the synthetic bone graft particles and polymer coating due to the GAA (or other form of AA) during packaging may be prevented to extend the shelf life of sheath 120. Preferably, drying step 180 may be conducted without the addition of heat when used with polymers having low melting points, such as but not limited to PCL having a melting point of approximately 60° C. In some preferred arrangements, coated sheath 20 may be dried by vacuum to quickly remove any moisture and residual acid while preserving the integrity of the synthetic bone graft particles and resultant polymer coating. It is also possible to dry coated sheath 20 with air at atmospheric pressure or forced air at an elevated pressure. Supplying compressed or otherwise forced air to coated sheath 20 is also less preferable than applying a vacuum as a sufficient amount of air to remove an acceptable amount of moisture may cause some of the polymer coating or synthetic bone graft particles to be removed from sheath 20. Following drying step 180, the moisture content within the polymer coating is preferably less than approximately 0.5% wt, and the synthetic bone graft particles are firmly adhered to sheath 20 by the remaining polymer coating. Optionally, prior to or, in some arrangements, in place of drying step 180, sheath 20 may be dried by way of moisture wicking through a capillary effect via direct contact with moisture on the sheath using a porous-like structure, such as but not limited to a brush, a cloth or paper towel, by way of a desiccant, or by way of another acceptable and preferably biocompatible drying agent known to those of ordinary skill in the art.

In preferred arrangements, after precipitation and drying of the polymer coating, the thickness of the polymer coating of prepared sheath 120 (or other prepared sheath such as prepared sheath 220) preferably may be in the range of less than approximately 100 μm, and more preferably in the range of 1 μm to 30 μm. As such, the polymer coating may have a thickness such that a significant number of synthetic bone graft particles coating sheath 20 are partially exposed, at their apices, through the polymer coating in addition to their exposure through the pores of the polymer coating. By way of this exposure, bioactivity may occur shortly after placement of prepared sheath 120 at a treatment site.

Referring now to FIG. 4A, when initially prepared as sheath and filament combination 110 placed onto the inserter, prepared sheath 120 is folded onto itself such that opposing portions 121, 122 of the prepared sheath, which may be in the form of legs, extend from end 123 in substantially parallel directions to each other. As shown in FIG. 4B, when deployed, prepared sheath 120 compresses, i.e., bunches, such that opposing portions 121, 122 are pushed in transverse directions to the inserter and away from each other, forming a substantially clover-like shape. In this deployed, compressed state, portions of the polymer coating may any of break up, crack, and stretch, providing further exposure of the synthetic bone graft particles and thus providing for greater bioavailability.

As further shown in FIG. 3B, during step 190, prepared sheath 120 is inserted into sterile packaging. In some arrangements, prepared sheath 120 may be placed into a pouch, which may be but is not limited to being made of aluminum foil, with a covering or leader, which may be but is not limited to being an olefin sheet such as but not limited to Tyvek® olefin sheets by E. I. du Pont de Nemours and Company. In some arrangements, the sheath (or sheath and filament combination) inserter described previously herein may be placed into the pouch with prepared sheath 120 disposed on the inserter and ready for placement into a treatment site. In alternative arrangements, prepared sheath 120 (or sheath and filament combination 110) may be separated from the inserter, and in such arrangements, the inserter may be placed in the same pouch as the sheath (or respective sheath and filament combination 110) or a separate sterile pouch. In any of these arrangements, a plurality of combinations or kits of prepared sheath 120 (or respective sheath and filament combination 110) and the inserter may be placed into sleeves. Preferably, when packaged and sterilized, the sterility assurance level (SAL) for prepared sheath 120 (or respective sheath and filament combination 110), or for the combination or kit of the sheath (or respective sheath and filament combination 110) and the corresponding inserter, is at or below 10⁻⁶ SAL To achieve this SAL, the packaged sheath 120 or packaged combination or kit of the sheath and the corresponding inserter preferably may be subjected to ethylene oxide (EtO) processing as well as periodic functional checks and lot release testing.

As shown in FIG. 5A, in one arrangement, sheath and filament combination 110A may be as described previously herein with respect to sheath and filament combination 110 in which the polymer coating is low molecular weight (LMW) PCL. As shown, the LMW PCL leads to hydroxyapatite deposition and crystallization (shown in whitish gray) on the surface of the sheath when exposed to living tissue fluids (as demonstrated through the use of simulated body fluids in the example shown), in particular at the pics, i.e., crossings, of fibers of the sheath. As shown in FIG. 5B, in another arrangement, sheath and filament combination 110B as described previously herein with respect to sheath and filament combination 110 in which the polymer coating is high molecular weight (HMW) PCL. The HMW PCL leads to hydroxyapatite deposition and crystallization (shown in whitish gray) on the surface of the sheath when exposed to living tissue fluids (as demonstrated through the use of simulated body fluids in the example shown), like the LMW PCL, but the hydroxyapatite deposition is substantially greater for the HMW PCL than for the LMW PCL, as shown by comparison of FIGS. 5A and 5B.

Referring now to FIG. 6, in another arrangement, sheath and filament combination 210 includes first filament 15A, second filament 15B, and prepared sheath 220 having an inner lumen through which the filaments are inserted. Prepared sheath 220 is generally formed by coating sheath 20 (see FIG. 1) with a polymer coating layer and then applying synthetic bone graft particles onto the polymer-coated sheath 20. In this manner, it is possible to add more exposed synthetic bone graft particles to sheath 20.

Referring now to FIG. 7, prepared sheath 220 is formed in the same or substantially the same manner as prepared sheath 120 with two exceptions. First, polymer solution coating step 150 is replaced with polymer solution coating step 250 in which polymer solution 135 coats sheath 20 without any synthetic bone graft particles coating the sheath. Second, graft coating step 140 is replaced with graft coating step 240 in which synthetic bone graft particles are applied to sheath 20 coated with polymer solution 135.

In some alternative arrangements, in place of or in addition to BA glass, the synthetic bone graft particles may include but are not limited to calcium phosphate or other bioactive additives. The calcium phosphate may be but is not limited to being tetra-calcium phosphate, di-calcium phosphate, dicalcium phosphate dihydrous, dicalcium phosphate anhydrous, tri-calcium phosphate, mono-calcium phosphate, β-tricalcium phosphate, α-tricalcium phosphate, oxypatite, hydroxypatite, and mixtures thereof. The other bioactive additives may include but are not limited to bone chips, demineralized bone chips or powder, living cells, lyophilized bone marrow, collagen, other bioactive proteins or growth factors, biologics, peptides, glycosaminoglycans, anti-inflammatory compounds, antibiotics, anti-microbial elements, and mixtures thereof.

In some alternative arrangements of sheath and filament combination 110, in place of or in addition to PCL, the barrier layer may be but is not limited to being replaced with another polymer such as polyglycolides (PGA), polylactic acids (PLA), polyethylene, polypropylene, polystyrene, poly(D,L-lactic-co-glycolide) (PLGA), polyglycolic acid (PGA), poly-L-Lactic acid (PL-LA), polysulfones, polyolefins, polyvinyl alcohol (PVA), polyalkenoics, polyacrylic acids (PAA), polyesters, lower alkyl cellulose ethers, methylcellulose, sodium carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethylcellulose, carboxymethyl cellulose, and mixtures thereof.

In some alternative arrangements, in place of or in addition to GAA, the coating solvent in the PCL or other polymer solution may be but is not limited to being at least one solvent of any of acetone, anisole, chloroform, methylene chloride, acetylchloride, 2,2,2 trifluoroethanol, trifluoroacetic acid, 1,2-Dochloroethane, mixtures thereof.

In some alternative arrangements, precipitating agents other than or in addition to the sodium phosphate buffer described previously herein may be used during formation of coated sheaths such as sheaths 120, 220. Such precipitating agents include but are not limited to water, ethanol, 1-propanol, isopropyl ether, 2-butanol, hexane, and mixtures thereof.

In some alternative arrangements, the combination of the polymer coating and the synthetic bone graft particles may be applied to any braided structure, especially such structures to be implanted into bone. Such braided structures may be but are not limited to ligament graft material, e.g., anterior cruciate ligament (ACL) graft material. The combination of the polymer coating and the synthetic bone graft particles may be applied to any such braided structure in the same manner that the combination of the polymer coating and the synthetic bone graft particles described previously herein as being applied to sheath and filament combination 110, 210.

All percentages and ratios used hereunder are by weight of the total composition and all measurements made are at about room temperature and normal pressure unless otherwise designated. “Room temperature” as defined hereunder means a temperature ranging between about 22° C. and about 26° C. All temperatures hereunder are in degrees Celsius unless specified otherwise.

As used herein, “consisting essentially of” means that the invention may include ingredients in addition to those recited in the claim, but only if the additional ingredients do not materially alter the basic and novel characteristics of the claimed invention. Preferably, such additional ingredients will not be present at all or only in trace amounts. However, it may be possible to include up to about 10% by weight of materials that could materially alter the basic and novel characteristics of the invention as long as the utility of the compounds (as opposed to the degree of utility) is maintained.

All ranges recited herein may include the endpoints, including those that recite a range “between” two values. Terms such as “about,” “generally,” “substantially,” and the like are to be construed as modifying a term or value such that it is not an absolute, but does not read on the prior art. Such terms will be defined by the circumstances and the terms that they modify as those terms are understood by those of skill in the art. This includes, at very least, the degree of expected experimental error, technique error and instrument error for a given technique used to measure a value.

It should be further understood that a description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 2.3, 3, 4, 5, 5.7 and 6. This applies regardless of the breadth of the range.

The terms such as “at least one of calcium phosphate or bioactive additive”, “calcium phosphate and/or bioactive additive”, and “bioactive additive and/or calcium phosphate” are used interchangeably throughout the remainder of the detailed description of this specification and should be understood to mean “calcium phosphate without bioactive additive, bioactive additive without calcium phosphate, or both calcium phosphate and bioactive additive.”

The terms “weight percent of the polymer solution” or “polymer concentration” and “weight percent of the mixture” as used herein have different meanings. The terms “weight percent of the polymer solution” or “polymer concentration” are defined as the weight of the polymer relative to the weight of the solvent. For example, a 10 wt % PCL-GAA solution may have 10 grams of PCL relative to 100 grams of GAA. In contrast, the term “weight percent of the mixture” is defined as the weight of a component of the mixture relative to the total weight of the mixture including the component. For example, a mixture of calcium phosphate and 10 wt % PCL-GAA solution having an amount of 10 wt % calcium phosphate may be 10 grams of calcium phosphate to 100 grams of the total weight of the mixture, i.e., the summed weight of calcium phosphate and 10 wt % PCL-GAA solution. The term “weight ratio” as used herein is defined as the weight of one component to the weight of another component. For example, a weight ratio of 6 grams of water to 2 grams of a 10% PCL-GAA solutions is 6:2.

The term ‘molecular weight’ as used herein in regards to a molecular weight of a polymer is a weight average molecular weight (M_(w)) unless otherwise specified. If a number average molecular weight of a polymer is used, it is indicated as M_(n).

The terms ‘foam’, ‘foam-like’, ‘foaming’ as used herein are not intended to describe a scaffold comprising a classically defined foam or formed by foaming, where a classically defined foam comprises a mass of small bubbles in a liquid. The terms ‘foam’, ‘foam-like’, or ‘foaming’ as used herein describe a physical appearance of a scaffold as similar to that of Styrofoam or seam-foam.

The terms “expansion”, or “expanding” as used herein to describe an increase in a volume or space that a group of polymer molecules occupy upon or while precipitating from a polymer solution or an increase in the volume of the scaffold formed upon precipitation. A scaffold formed from a precipitated and expanded polymer initially present in a polymer solution, or a precipitated and expanded polymer initially present in a mixture including the polymer solution and at least one of calcium phosphate or a bioactive additive, can have a structure that is foam-like and/or amorphous.

Methods

Described herein are methods of making a scaffold in accordance with some embodiments of the present invention. In one embodiment, a method of preparing a scaffold may include dissolving a polymer in a solvent to form a polymer solution; adding a precipitating agent to the polymer solution; precipitating and expanding the polymer from the polymer solution to form the scaffold; and removing the solvent from the scaffold.

The method described herein can employ a two phase system to form a scaffold. The two phase system may comprise a polymer solution as one phase and precipitating agent as the other phase. Chemical reactivity resulting from the precipitating agent being introduced into the polymer solution induces rapid intermixing, precipitation and expansion of the polymer to form the scaffold. Scaffolds can be formed within minutes and can be relatively homogeneous, amorphous, non-crystalline, foam-like, and porous, having irregularly-sized holes and channels. The method does not use a foaming agent to achieve a scaffold having a foam-like structure. In one embodiment, the polymer solution can be a viscous solution, such as PCL dissolved in glacial acetic acid. In one embodiment, the precipitating agent can be water, a non-organic low viscosity solvent.

The polymer may include one or more polymers as discussed herein. A solvent may include any suitable solvent that is capable of dissolving the polymer, and may vary depending on the polymer that is being dissolved. Exemplary solvents may include, without limitation, one or more of glacial acetic acid (GAA), anisole, chloroform, methylene chloride, acetylchloride, 2,2,2 trifluoroethanol, trifluoroacetic acid, and/or 1,2-Dochloroethane. Other solvents that may be utilized with the inventive methods may be found in Bordes, C., et al., 2010, International J. Pharmaceutics, 383, 236-243, which is incorporated herein by reference.

The polymer can be dissolved in the solvent in any suitable concentration necessary to produce a scaffold having the desired properties. The concentration of polymer in the polymer solution may influence mechanical properties of the resulting scaffold, such as flexibility and ability to retain calcium phosphate or bioactive additive. In some embodiments, physical and chemical properties of the polymer solution, such as molecular weight, specific gravity, polarity, or the like, may have an influence on the morphology of the scaffold formed therefrom. In some embodiments, morphology of the scaffold may be modified, at least partially, by identity of polymer and/or solvent.

The concentration of polymer in solution may depend on the polymer and solvent used. For example, the solubility of PCL in many different solvents was reported in Bordes, C., et al., where it is noted that depending on the solvent used, PCL having a range of molecular weights may be soluble at up to 50 wt % solutions. In some embodiments, the polymer concentration may range from about 1 wt % to about 50 wt %, relative to the weight of solvent, preferably from about 5.0 wt % to about 15 wt %, more preferably from about 7.0 wt % to about 10 wt % of the polymer solution. The polymer concentration range may be above 50 wt % in some embodiments. In some embodiments, the polymer may be present in a saturated amount or supersaturated amount in the polymer solution. In some embodiments, the polymer may be PCL and the solvent may be GAA, where PCL is dissolved in GAA ranging from about 7.0 wt % to greater than about 10 wt %, or to a saturated level. In some embodiments, the saturated level may be in excess of about 10 wt % but less that about 15 wt % for PCL dissolved in GAA. As shown in FIGS. 8A-8D, PCL solutions ranging from about 7.0 wt % to up to a saturated level (labeled as 10%-15%) can produce scaffolds that retain a shape of a mold in which they were made, and retain calcium phosphate, which is embedded in the scaffold during the molding process. In some embodiments, higher concentrations of PCL in solution may be achieved using anisole as a solvent, instead of GAA. In such an embodiment, PCL may be dissolved in anisole from about 10 wt % to about 50 wt %. For example, PCL having a molecular weight of about 14,000 g/mol was soluble in anisole at up to 50% wt %, and PCL having a molecular weight of 65,000 g/mol may be dissolved at 10 wt % but less than 50 wt %.

The method may include precipitating the polymer from the polymer solution to form the scaffold. Alternatively, when calcium phosphate and/or bioactive additive is used (described further below), the polymer may be precipitated from a mixture formed from calcium phosphate and/or bioactive additive added to the polymer solution. The precipitation of the polymer from the polymer solution may generate a scaffold that is fluffy, amorphous, absorbent, and low density, unlike higher density scaffolds generated using other methods. A low density scaffold may be more porous, deformable, drapable, compressible, not load bearing to a significant extent, and able to tear apart by hand, in contrast to a high density scaffold. A high density scaffold would be less porous, somewhat load bearing, rigid and marginally, if at all drapable, not very compressible, and difficult, if not impossible to tear apart by hand, compared with a low density scaffold. In some embodiments, scaffolds of medium or high density can also be achieved using methods discussed herein. In some embodiments, the scaffolds can resist hand pressure to some extent as well as retaining fluid even when a force ten or more times its weight is applied. In some embodiments, compression resistance of the scaffold may depend on any or all of polymer concentration in the polymer solution, polymer molecular weight, and amount of calcium phosphate and/or bioactive additive used.

The polymer may be precipitated by contacting the polymer solution or the mixture with a precipitating agent to form the scaffold. In some embodiments, the entire scaffold can be formed by contacting the polymer solution or mixture with the precipitating agent. For example, the scaffold is not formed piecewise by using a precipitating agent to precipitate a portion of the polymer, and removing solvent to precipitate another portion of the polymer. In some embodiments, a scaffold having a foam-like and/or amorphous structure is not formed in the absence of a precipitating agent. For example, removal of solvent to precipitate the polymer in the absence of a precipitating agent does not form a scaffold having a foam-like and/or amorphous structure. Exemplary precipitating agents can include, without limitation, water, ethanol, 1-propanol, isopropyl ether, 2-butanol, hexane, or combinations thereof. The total time to precipitate a scaffold can be on the order of minutes. In some embodiments, a precipitation time may range from about 1 minute to about 30 minutes. In other embodiments, the precipitation time may range from about 5 minutes to 25 minutes. In yet other embodiments, the precipitation time may range from 10 minutes to 20 minutes. In yet other embodiments, a precipitation time up to 1 hour may be utilized.

The polymer may be precipitated in various ways. For example, in some embodiments where a mold is used, the precipitating agent may be initially added drop wise to an exposed surface of the polymer solution disposed in the mold. The mold may, optionally, then be submerged in the precipitating agent. In some embodiments, when the polymer solution is present on a substrate, the polymer solution including the substrate may be immersed in the precipitating agent to precipitate the polymer to form the scaffold. In some embodiments, the precipitating agent may be sprayed or misted onto a surface of the polymer solution or a mixture including the polymer solution and at least one of calcium phosphate or bioactive additive. In some embodiments, the precipitating agent may be flowed or poured onto the surface of the polymer solution or the mixture of polymer solution and at least one of calcium phosphate or bioactive additive. The amount of precipitation agent added and/or its speed of addition may strongly influence the foam-like qualities and density of the resulting scaffold.

In some embodiments, an order in which method steps are performed may determine the morphology of a resulting scaffold. One exemplary embodiment is described in Experimental Example 6 below. Under some conditions, a scaffold formed by dropwise adding of a precipitating agent to a polymer solution may result in a fluffy, amorphous, foam-like scaffold. Under some conditions, when the same amount of polymer solution is dropwise added to a precipitating agent, the resulting scaffold can be irregularly shaped and has non-homogenous density.

The polymer can expand upon or while precipitating from the polymer solution or a mixture including the polymer solution and at least one of calcium phosphate or a bioactive active. In some embodiments, precipitation and expansion of the polymer occur simultaneously. In some embodiments, the amount of precipitating agent and/or the speed at which it is added may cause both precipitation and expansion of the scaffold. One exemplary embodiment is described in Experimental Example 6. When no precipitating agent is used, and the scaffold is precipitated through air drying, the scaffold is dense, slightly flexible when manipulated by hand, and appears to have little or no porosity based on visual inspection. As an amount of precipitating agent is increased relative to the amount of PCL solution, the resulting scaffold is less dense, porous, fluffy, and Styrofoam-like in appearance. If the amount of precipitating agent is increased too far relative to the amount of PCL solution, the scaffold continues to expand, but can expand into scaffolds of irregular shapes. In some embodiments, a weight ratio of precipitating agent to a polymer solution may range from about 0.05:1 to about 3.5:1. In some embodiments, the weight ratio may range from about 0.5:1 to 3:1. In yet other embodiments, the weight ratio may range in excess of 3.5:1.

The expansion of the scaffold can be controlled by an amount of precipitating agent added. The expansion can alter the density and/or porosity of the scaffold relative to a scaffold where no precipitating agent is used. In some embodiments, the scaffold has a thickness that may be at least about 2 times that of a scaffold where no precipitating agent is used. In some embodiments, the scaffold has a thickness that may be at least about 3 times up to about 8 times. In yet another embodiment, the scaffold has a thickness that may be at least about 1 order of magnitude greater than that of a scaffold where no precipitating agent is used. In yet another embodiment, the scaffold has a thickness that is greater than about 1 order of magnitude may be utilized.

In some embodiments, a density of the scaffold may have an inverse linear relationship with thickness of the expanded scaffold. For example, a scaffold made using a precipitating agent may have about 2 times the thickness of a scaffold made without the use of a precipitating agent, and about 50% of the density. In some embodiments, the density of a scaffold made using a precipitating agent may range from about 90% to about 14% of the density of a scaffold made without using a precipitating agent. In some embodiments, the density may range from about 70% to about 14%. In other embodiments, the density may range from about 50% to 14%. In yet other embodiments, the density may range from about 40% to about 14%. In yet other embodiments, the density may range from about 29% to about 14%. In yet another embodiment, the density may be less than 14%. In yet another embodiment, a density of about 11% or less may be utilized. However, the relationship may not necessarily be inverse linear in all cases, and may depend on the shape of the mold used to make the scaffold.

The porosity of a scaffold made with a precipitating agent may be greater than that of a scaffold made without a precipitating agent. In some embodiments, as density of the scaffold decreases, such as when an amount of precipitating agent added is increased, a fluid holding capacity, or porosity, can increase.

In some embodiments, surface topology of the scaffold and perhaps to some extent scaffold thickness may be controlled based on how the precipitating agent is added to the surface of the mixture. For example, a uniform, fine spray may yield a flat, dense surface. In other embodiments, a slow, drop wise pipetting can result in a dimpled, fluffy surface. Slow to sudden submersion to various depths below the surface of the precipitating agent may result in scaffolds having differing degrees of fluffy, sea foam-like surfaces and thicknesses. When precipitating agent addition is carefully controlled by drop wise addition or a fine water spray, the dimensions of the resulting scaffolds can roughly approximate that of the molds in which they are cast. In some embodiments, a mold may have a thickness ranging from about 5 mm to about 30 mm. In some embodiments, a mold has a thickness exceeding about 30 mm. In some embodiments, any suitable thickness of mold can be utilized. In some embodiments, depending on a method of scaffold precipitation the scaffold may exceed the thickness of the mold by one or more millimeters. The method may include adding at least one of calcium phosphate and/or bioactive additive to the polymer solution to form a mixture. Any suitable calcium phosphate or bioactive additive may be utilized. The mixture may vary from a solution, or suspension, or a paste, depending on the application. For example, when calcium phosphate and/or bioactive glass particles are added, the mixture may be a suspension. Alternatively, if a soluble calcium phosphate and/or bioactive additive is used, the mixture may be a solution. In some embodiments, the mixture may be viscous, such as a paste, which can be obtained by controlling the amount of polymer solution relative to calcium phosphate or bioactive additive, as well as the size of the particle component of the paste. A paste may be utilized, for example, when coating the mixture on a substrate. However, solutions or suspension of the mixture can also be used to coat substrates.

The amount of calcium phosphate and/or bioactive additive in the mixture may vary depending on the application. In some embodiments, the amount of calcium phosphate may range from about 15 to about 50 wt %, based on the total weight of the mixture. The total weight of the mixture may be the summed weight of the individual components of the mixture, such as calcium phosphate, bioactive additive, and polymer solution. In some embodiments, the amount of calcium phosphate may range from about 15 wt % to about 40 wt %, preferably about 20 wt % to about 40 wt %. In some embodiments, the mixture may be a paste, when calcium phosphate exceeds about 20 wt %. An amount of a bioactive additive present in the mixture may be dependent on the identity of the bioactive additive, and may range from about 0.001 wt % to about 80 wt % of the mixture. For example, a bioactive additive that is a growth factor may be present in a very low to low concentration, for example, ranging from about 0.001 wt % to about 10 wt % of the mixture. For example, a bioactive additive that is a structural component, such as collagen, may be present in a higher concentration, for example, ranging from about 10 wt % to about 80 wt % of the mixture.

The amount of polymer solution used relative to other components, such as the calcium phosphate and/or the bioactive additive, may influence the properties. For example, as shown in FIGS. 9A-9F, for a 10 wt % PCL-GAA solution, an amount of calcium phosphate of at least about 19 wt %, relative to the 10 wt % PCL-GAA solution, can produce a scaffold that retains a shape of the mold in which the scaffold was made, and also retains the calcium phosphate. In contrast, below about 19 wt % in this exemplary embodiment, the scaffold fails to retain the shape of the mold, and at least some of the calcium phosphate.

The mixture may be formed in various ways. In some embodiments, the polymer solution and at least one of the calcium phosphate or bioactive additive can be combined to form the mixture, and then the mixture may be deposited on a substrate, in a mold, or in any suitable apparatus to shape a scaffold. In one embodiment, calcium phosphate is deposited in a mold, and then the polymer solution is added to the mold to form the mixture. In one embodiment, a substrate is dipped in the polymer solution, and then the coated substrate is dipped in, or otherwise coated with, calcium phosphate. Similar methods of forming a mixture can be applied for bioactive additives.

In some embodiments, the precipitating agent may be frozen in the calcium phosphate and/or bioactive additive. For example, prior to adding the calcium phosphate and/or bioactive additive to the polymer solution, the calcium phosphate and/or bioactive additive may be soaked with the precipitating agent, and frozen. The frozen calcium phosphate and/or bioactive additive may then be mixed with the polymer solution to form the mixture. The frozen calcium phosphate and/or bioactive additive will thaw in the mixture and release the precipitating agent which can result in precipitation of the polymer from the mixture to form a scaffold.

In some embodiments, the polymer solution may be frozen and then added to the precipitating agent. In other embodiments, the mixture of the polymer solution and calcium phosphate and/or the bioactive additive may be frozen and then added to the precipitating agent. For example, the polymer solution may be mixed with calcium phosphate and/or bioactive additive to form the mixture. The mixture may then be frozen, and then contacted with the precipitating agent. As the frozen mixture thaws, precipitation of the polymer can occur to form a scaffold.

In one embodiment, a scaffold may be formed with a bioactive additive that includes living cells. For example, such a scaffold may be used to deliver the living cells to tissues or implants. The living cells may be frozen in an appropriate freezing medium for cells. The frozen living cells may be further encased in a frozen solution containing sodium hydroxide or another base to form a frozen formulation. The frozen formulation could be submerged in the polymer solution to form the mixture. As the base and polymer mix to reach pH neutrality, polymer can precipitate around and encase the living cells to form a scaffold.

The method may comprise removing the solvent and/or precipitating agent from the scaffold. For example, after precipitation of the polymer the solvent may be removed from the resulting scaffold by any suitable method. In some embodiments, the precipitating agent may be removed when the solvent is removed. Removal of the solvent and/or precipitating agent may occur over any suitable time frame. This time frame may depend, for example, on the size of the scaffold, amount of solvent and/or precipitating agent used, the method of removal used, and the like. In some embodiments, removal of the solvent and/or precipitating agent may range up to about 24 hours. In some embodiments, removal of the solvent ranges from about 5 minutes to about 20 hours. In some embodiments, removal of the solvent ranges from about 5 minutes to about 15 hours. In some embodiments, removal of the solvent ranges from about 5 minutes to about 10 hours. In some embodiments, removal of the solvent ranges from about 5 minutes to about 5 hours. In some embodiments, removal of the solvent ranges from about 5 minutes to about 3 hours. In some embodiments, removal of the solvent ranges from about 20 minutes to about 1 hour. In yet other embodiments, removal of the solvent range from about 15 minutes to about 30 minutes. In one embodiment, the solvent may be removed by rinsing, which may result in dilution and removal of the solvent. For example, the scaffold may be submerged in water during the rinsing process. In one embodiment, the solvent may be removed by evaporating the solvent under room temperature and ambient pressure conditions. In other embodiments, removal of the solvent may be accelerated by exemplary processes, such as exposure to temperatures below the melting point of the polymer of the scaffold, and also below a temperature that may inactivate, denature, or otherwise destroy any other component of the scaffold, as well as ambient forced air, vacuum drying, lyophilization, or other methods that can remove the solvent but do not untowardly affect any other component of the scaffold. In one example, removal of a solvent in a PCL-containing scaffold may occur at temperatures below about 60° C. because PCL melts at about 60° C. The above-described methods for removal of the solvent may be used alone or in combination.

Further, for applications where the scaffold is used within the human body, sterilization may need to be performed. One common sterilization method is gamma-beam irradiation. Polymers, such as PCL, and calcium phosphate are amenable to gamma-beam irradiation. In some embodiments, gamma-beam irradiation may affect the molecular weight and/or other aspects of the chemical structure of the plastic comprising the scaffold and thus the physical characteristics of the scaffold even when polymers such as PCL are used. Therefore, parameters of the method, such as polymer concentration, molecular weight and the like, may be modified to account for a sterilization process.

The methods described herein can be further exemplified as discussed in the Examples below.

Scaffold

The scaffolds formed herein have significant porosity, allowing them to soak up and retain biological fluids like blood or bone marrow aspirate, which are often added to bone regeneration scaffolds prior to implantation in patients. Also, their lower density, foam-like composition makes them easier to mold by hand and compress to fit into a hole or defect in bone. It also may be speculated that the lower density, foam-like nature of the scaffolds described in the present invention may allow for their more rapid in vivo degradation and resorption in comparison with PCL-based scaffolds formed using other methods.

The scaffolds described herein are in the form of a polymer matrix. The scaffolds produced using the methods described herein may be different in terms of final composition and physical properties as compared with scaffolds manufactured by other methods. The scaffolds described herein may have a foam-like appearance. The scaffolds may have a relatively amorphous structure. The scaffolds may be non-crystalline. The density and porosity of the scaffolds can be controlled by the methods described herein to control a rate of bioresorption of the scaffold in vivo. In some embodiments, the plastic component(s) of the scaffolds produced using the methods discussed herein may not have a uniform or homogeneous fully interconnected pore structure. Moreover, in some embodiments, the scaffolds may have calcium phosphate and/or bioactive additive embedded in the polymer matrix. In some embodiments, though embedded in the polymer matrix, calcium phosphate and/or bioactive additive may retain at least some characteristic properties, such as porosity.

In some embodiments, the scaffold may be a polymer matrix, for example, made of only polymer and absent of additional materials embedded within the matrix and/or on the surface thereof, for example, as shown in FIGS. 17A and 17B and discussed herein in Example 5-1. Such a scaffold may be utilized to hold open or expand a space prior to organ transplant, to inhibit or block tissue adhesions following surgery, or other medical applications that do not involve orthopedic applications, such as bone regeneration or bone replacement. Further, it is contemplated that such scaffolds may be utilized in non-medical applications, such as for thermal or electrical insulation, packing materials, or the like.

In some embodiments, the scaffold includes the polymer matrix and at least one of calcium phosphate or a bioactive additive embedded therein and/or disposed on the surface thereof. The calcium phosphate may be any number of calcium phosphate materials as discussed herein. The bioactive additive may be any number of additives, such as collagen, bioactive glass, and/or other additives as discussed herein. In some embodiments, the scaffold does not include any animal-derived materials, such as collagen, living cells, or other animal-derived materials. Among other reasons, the absence of animal-derived materials may prevent immunoreactivity, transmission of viral, bacterial, or prion infections and/or satisfy religious concerns in regards to animal-derived materials, when such scaffolds are implanted as medical devices into humans.

The scaffold may include a substrate. For example, the substrate may modify the physical properties of the scaffold, such as a three dimensional substrate formed from a stiff polymer to improve mechanical strength of the scaffold. Exemplary substrates may include a mesh or screen, such as those made of a metal, plastic, or fabric, a porous polymer substrate, a bone suture anchor, which may be filamentous and/or comprised of a textile, a porous metal implant, a tissue autograft or allograft or derivatives therefrom and/or living tissue.

The scaffold can have any suitable shape, for example, such as a sheet, a rectangle, a wedge, a cylinder, a square, a sphere, and the like, or the shape may be irregular, such as sized to fit a particular application, such as a size and/or shape of a portion of bone being filled. A mold, or another apparatus, such as a substrate, may be used to make a scaffold having any suitable shape.

Polymer

The polymer used in the methods described herein and scaffolds is not particularly limiting, though polymers that are biocompatible and can be dispersed and/or dissolved in a solvent are preferred.

Any suitable resorbable biocompatible polymer may be used in accordance with the present invention. Examples of suitable polymers include, without limitation, polycaprolactones (PCL), polyglycolides (PGA), polylactic acids (PLA), polyethylene, polypropylene, polystyrene, poly(D,L-lactic-co-glycolide) (PLGA), polyglycolic acid (PGA), poly-L-Lactic acid (PL-LA), polysulfones, polyolefins, polyvinyl alcohol (PVA), polyalkenoics, polyacrylic acids (PAA), polyesters, lower alkyl cellulose ethers, methylcellulose, sodium carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethylcellulose, carboxymethyl cellulose, and mixtures thereof. In other embodiments, the biocompatible polymer may further contain gelatin and other suitable polymers described, for example, in U.S. Pat. Nos. 7,189,263; 7,534,451; 7,531,004; and 8,287915, which are incorporated herein by references in their entireties.

In some embodiments, the polymer may have a molecular weight (MW) ranging from about 3,000 g/mol to about 150,000 g/mol. In one embodiment, the polymer may have a MW ranging from about 3,000 g/mol to about 120,000 g/mol. In yet another embodiment, the polymer may have a MW ranging from about 3,000 g/mol to about 100,000 g/mol. In yet another embodiment, the polymer may have a MW ranging from about 3,000 g/mol to about 80,000 g/mol. In yet another embodiment, the polymer may have a molecular weight (MW) ranging from about 14,000 g/mol to about 65,000 g/mol. In one embodiment, the polymer may have a MW ranging from about 40,000 g/mol to about 50,000 g/mol. In some embodiments, molecular weights above 150,000 g/mol can be utilized. In some embodiments, the polymer may have a molecular weight (M_(n)) ranging from greater than about 45,000 g/mol up to about 80,000 g/mol. In some embodiments, M_(n) above 80,000 g/mol can be utilized. For example, different polymers and different solvents can allow for polymers having higher MW to dissolve to form a polymer solution.

Calcium Phosphate

Various calcium phosphates are contemplated and include, for example, tetra-calcium phosphate, di-calcium phosphate, dicalcium phosphate dihydrous, dicalcium phosphate anhydrous, tri-calcium phosphate, mono-calcium phosphate, β-tricalcium phosphate, α-tricalcium phosphate, oxypatite, hydroxypatite, and mixtures thereof. However, for the sake of brevity, “calcium phosphate” includes any calcium salt known to those skilled in the art. The preparation of various forms of calcium phosphate for use in the present invention is described in U.S. Pat. Nos. 5,939,039, 6,383,519, 6,521,246, and 6,991,803, which are incorporated herein by reference in their entireties. Exemplary calcium phosphate products may include Vitoss® Bone Graft Substitutes, such as Vitoss® micromorsels (1-2 mm) or Vitoss® subfines (<1 mm) (Stryker Orthobiologics, Malvern, Pa.).

Some embodiments of the scaffold may partially comprise materials, or morsels, resulting from an oxidation-reduction reaction. These materials may be produced by methods comprising preparing an aqueous solution of a metal cation and at least one oxidizing agent. The solution is augmented with at least one soluble precursor anion oxidizable by said oxidizing agent to give rise to the precipitating agent oxoanion. The oxidation-reduction reaction thus contemplated is conveniently initiated by heating the solution under conditions of temperature and pressure effective to give rise to said reaction. The oxidation-reduction reaction can cause at least one gaseous product to evolve and the desired intermediate precursor mineral to precipitate from the solution. A reactive blend may be imbibed into a material that is capable of absorbing it to produce a porous mineral. It may be preferred that the material have significant porosity, be capable of absorbing significant amounts of the reactive blend via capillary action, and that the same be substantially inert to reaction with the blend prior to its autologous oxidation-reduction reaction.

The intermediate precursor mineral thus prepared can either be used “as is” or can be treated in a number of ways. Thus, it may be heat-treated greater than about 800° C. or, preferably, greater than about 1100° C. in accordance with one or more paradigms to give rise to a preselected crystal structure or other preselected morphological structures therein. In some embodiments, the oxidizing agent is nitrate ion and the gaseous product is a nitrogen oxide, generically depicted as NO_(x)(g). The precursor mineral provided by the present methods be substantially homogenous. As used in this context, substantially homogenous means that the porosity and pore size distribution throughout the precursor mineral is the same throughout.

In some embodiments, the intermediate precursor mineral may be any calcium salt. Subsequent modest heat treatments convert the intermediate material to, e.g., novel monophasic calcium phosphate minerals or novel biphasic β-tricalcium phosphate (β-TCP)+type-B, carbonated apatite (c-HAp) [β-Ca₃(PO₄)₂+Ca₅(PO₄)_(3-x)(CO₃)x(OH)] particulates. More preferably, the heat treatment converts the intermediate material to a predominantly β-TCP material.

In one embodiment, the calcium phosphate is □-TCP. In some embodiments, the calcium phosphate is porous. In some embodiment, the calcium phosphate contains micro-, meso-, and macroporosity. In some embodiment, the porosity of the calcium phosphate is interconnected. Macroporosity is characterized by pore diameters greater than about 100 μm and, in some embodiments, up to about 1000 μm to 2000 μm. Mesoporosity is characterized by pore diameters between about 10 μm and 100 μm, while microporosity occurs when pores have diameters below about 10 μm. In some embodiments, that macro-, meso-, and microporosity occur simultaneously and are interconnected in products. It is not necessary to quantify each type of porosity to a high degree. Rather, persons skilled in the art can easily determine whether a material has each type of porosity through examination, such as by mercury intrusion porosimetry, helium pycnometry or scanning electron microscopy. While it is certainly true that more than one or a few pores within the requisite size range are needed in order to characterize a sample as having a substantial degree of that particular form of porosity, no specific number or percentage is called for. Rather, a qualitative evaluation by persons skilled in the art shall be used to determine macro-, meso-, and microporosity.

In some embodiments, the calcium phosphate is in the form of particles or morsels and may contain a porous structure as described herein.

It will be appreciated that in some embodiments, the overall porosity of the calcium phosphate will be high. This characteristic is measured by pore volume, expressed as a percentage. Zero percent pore volume refers to a fully dense material, which, perforce, has no pores at all. One hundred percent pore volume cannot meaningfully exist since the same would refer to “all pores” or air. Persons skilled in the art understand the concept of pore volume, however and can easily calculate and apply it. For example, pore volume may be determined in accordance with Kingery, W. D., Introduction to Ceramics, Wiley Series on the Science and Technology of Materials, 1^(st) Ed., Hollowman, J. H., et al. (Eds.), Wiley & Sons, 1960, p. 409-417, which provides a formula for determination of porosity. Expressing porosity as a percentage yields pore volume. The formula is: Pore Volume=(1−f_(p)) 100%, where f_(p) is fraction of theoretical density achieved.

Porosity can be measured by Helium Pycnometry. This procedure determines the density and true volume of a sample by measuring the pressure change of helium in a calibrated volume. A sample of known weight and dimensions is placed in the pycnometer, which determines density and volume. From the sample's mass, the pycnometer determines true density and volume. From measured dimensions, apparent density and volume can be determined. Porosity of the sample is then calculated using (apparent volume-measured volume)/apparent volume. Porosity and pore size distribution may also be measured by mercury intrusion porosimetry.

Pore volumes in excess of about 30% may be achieved while materials having pore volumes in excess of 50% or 60% may also be routinely attainable. Some embodiments of the calcium phosphate may have pore volumes of at least about 70%. Some embodiments that may be preferred have pore volumes in excess of about 75%, with 80% being still more preferred. Some embodiments may have pore volume greater than about 90%, more preferably greater than about 92%. In some preferred cases, such high pore volumes are attained while also attaining the presence of macro- meso- and microporosity as well as physical stability of the materials produced.

It will be appreciated that the morsel size and content will be selected based on the desired application. For example, it may be necessary for the scaffold to have one or more properties, such as elasticity, stiffness, tensile strength, and in vivo degradation rate. Morsel size and content of the morsels within the scaffold may be selected with one or more of those properties in mind. The morsel size can range from about 100 μm to 2,000 μm, from about 200 μm to 900 μm, and from about 212 μm to about 850 μm. Unless otherwise specified, morsel size as used herein refers to the sieve size used to partition the calcium phosphate morsels.

Due to the high porosity and broad pore size distribution (1 μm to 2000 μm) of the morsels, the scaffold may be able to wick/soak/imbibe materials very quickly, and also be capable of retaining them. Materials may include a variety of fluids including blood, bone marrow aspirate, saline, antibiotics and proteins such as bone morphogenetic proteins (BMPs). Materials can also be imbibed with cells (e.g., fibroblasts, mesenchymal, stromal, marrow and stem cells), platelet rich plasma, other biological fluids, and any combination of the above. The scaffold can hold, maintain, and/or retain fluids once they are imbibed, allowing for contained, localized delivery of imbibed fluids. This capability has utility in cell-seeding, drug delivery, and delivery of biologic molecules as well as in the application of bone tissue engineering, orthopedics, and carriers of pharmaceuticals.

Bioactive Additive

Various bioactive additives are contemplated, including natural and synthetic bioactive additives. Exemplary bioactive additives may include bioactive glass, bone chips, demineralized bone chips or powder, living cells, lyophilized bone marrow, collagen, other bioactive proteins or growth factors, biologics, peptides, glycosaminoglycans, anti-inflammatory compounds, antibiotics, anti-microbial elements, small biomolecules, active pharmaceutical ingredients, antibodies, and/or mixtures thereof.

The type of collagen used is not particularly limiting, and can include native fibrous insoluble human, bovine, porcine, or synthetic collagen, soluble collagen, reconstituted collagen, or combinations thereof. Some embodiments of the scaffolds do not contain collagen.

“Bioactive glass” as used herein may be any alkali-containing ceramic, glass, glass-ceramic, or crystalline material that reacts as it comes in contact with physiologic fluids including, but not limited to, blood and serum, which leads to bone formation. In some embodiments, bioactive glasses, when placed in physiologic fluids, form an apatite layer on their surface. Examples of bioactive glasses suitable for use are described in U.S. Pat. No. 5,914,356, incorporated herein by reference. Suitable bioactive materials also include 45S5 glass and glass-ceramic, 58S5 glass, S53P4 glass, apatite-wollastonite containing glass and glass-ceramic. The bioactive glass may be a glass-ceramic composition comprising heterogeneous particles having an irregular morphology and regions of combeite crystallites (“Combeite glass-ceramic” having the chemical composition Na₄Ca₃Si₆O₁₆(OH)₂). In some embodiments, the bioactive glass comprises about 5-50% by volume of regions of combeite crystallites. Bioactive glasses suitable for use may be those compositions comprising calcium-phosphorous-sodium-silicate and calcium-phosphorous-silicate. Such bioactive glasses include NovaBone and NovaBone-AR, distributed by NovaBone Products, LLC, Alachua, Fla. Further bioactive glass compositions that may be suitable for use are described in U.S. Pat. No. 6,709,744, which is incorporated herein by reference.

In some embodiments, resorption of bioactive glass particles of about 150 μm or less occurs as silica as released within the apatite gel layer, while larger particles are eventually broken down by osteoclasts (Goasin, A. Bioactive Glass for Bone Replacement in Craniomaxillofacial Reconstruction, Plastic and Reconstructive Surgery (2004) Vol. 114, No. 2, pp. 590-593). The scaffold may provide appropriate bone growth independent of the inclusion of bioactive glass. The role of the bioactive glass in the scaffold described herein may be stimulatory to osteoblasts, and as such, large particles of glass (>150 μm) may not be necessary, and thus the particles which are resorbed via dissolution are preferred. However, all sizes of resorbable glass particles are contemplated as suitable.

Particle size measurement is well known in the art. Unless otherwise specified, particle size as used herein refers to the sieve size used to partition the glass particles. The bioactive glass particles may range in size from about 20 μm to about 200 μm, or about 100 μm or less, or about 150 μm or less, or about 30 μm to about 200 μm. The bioactive glass particles may be bimodal in nature, with distinct particles in the size range 32 μm-90 μm and particles in the size range 90 μm-150 μm. The bioactive glass particles may be solid or may even be porous. In some embodiments, the bioactive glass is nonporous.

EXAMPLES Experimental Example 1: Scaffold Quality as a Function of Polymer Concentration

Experimental Example 1 studies scaffold quality as a function of polymer concentration in the polymer solution. Examples 1-1 through 1-3, the results of which are depicted in FIGS. 8A-8C, were made using the same methods, except different concentrations of polymer are used in the polymer solution in each Example. Comparative Example 1-1, the result of which is depicted in FIG. 8D, was made using the same methods, except using a polymer concentration lower than that of Examples 1-1 through 1-3.

A PCL filament-derived material for 3D printing (available from Makerbot, M_(n)=about 50,000 g/mol) The PCL filament-derived material was cut into small pieces prior to further use. Though the Examples herein used PCL filament-derived material, other types of PCL materials may be contemplated, for example, such as PCL pellets.

Example 1-1: Saturated PCL Solution

About 1.5 gram of PCL was added to about 10 g of glacial acetic acid (GAA) in a 50 ml plastic sample tube and the mixture was agitated over the course of several hours by intermittently vortexing using a Fisher Scientific Vortex Mixer to form a PCL solution. Other forms of mixing or sample agitation may be contemplated to solubilize the PCL. The PCL-GAA solution has a concentration of PCL greater than about 10 wt % and less than about 15 wt %. Concurrently, about 3.4 g of calcium phosphate (Vitoss® micromorsels, 1-2 mm, available from Stryker Orthobiologics) were placed into a mold (Aluminum, rectangular shaped, about 1.0 inch wide×4.0 inches long× 7/18 inches deep), where the mold was sprayed with cooking oil and excess oil wiped away with a kimwipe prior to adding the calcium phosphate. About 12 g of the 10 wt %-15 wt % PCL-GAA solution was added to the mold containing the calcium phosphate, and the mixture of PCL, GAA, and calcium phosphate was allowed to sit for about 5 min in the mold. After which, about 1 to about 2 grams of water was added drop wise to the surface of the mixture, and the mixture was allowed to incubate for about 15 to about 30 minutes at room temperature and ambient pressure conditions. After the incubation period, the mold was submerged to about 1 to about 2 mm below the surface of a water bath at about room temperature and allowed to incubate for about 15 to about 30 minutes. After the incubation period, and while submerged, the lateral edges of the scaffold were separated from the mold using a metal spatula. The mold and scaffold were further incubated for about 15 to 30 minutes. After the incubation period the scaffold was removed from the mold and air dried. The scaffold lost more than twice its weight during drying. The resulting scaffold is depicted in FIG. 8A.

Example 1-2: 10% PCL Solution

Example 1-2 is made using the same procedure described for Example 1-1, except about 1 g of PCL is added to about 10 g of GAA to form a 10 wt % PCL-GAA solution. The resulting scaffold is depicted in FIG. 8B.

Example 1-3: 7.5% PCL Solution

Example 1-3 is made using the same procedure described for Example 1-1, except about 0.75 g of PCL is added to about 10 g of GAA to form a 7.5 wt % PCL_GAA solution. The resulting scaffold is depicted in FIG. 8C.

Comparative Example 1-1: 5.0% PCL Solution

Comparative Example 1-1 is made using the same procedure described for Example 1-1, except about 0.5 g of PCL is added to about 10 g of GAA to form a 5 wt % PCL-GAA solution. The resulting scaffold is depicted in FIG. 8D.

As shown in FIGS. 8A-8D, the scaffolds of Examples 1-1 through 1-3, and Comparative Example 1-1 have bright white, styrofoam-like appearance, and in some cases exhibit a fluffy, sea-foam like surface. The scaffolds roughly approximate the size of the mold from which the scaffolds were cast.

The concentration of PCL in the polymer solutions was found to affect the physical characteristics of the resulting scaffold. Intact scaffolds, e.g., those that could easily be removed from the mold and retained a large fraction of the calcium phosphate added, were produced using 10 wt %-15 wt %, 10 wt %, and 7.5 wt % PCL-GAA solutions as shown in FIGS. 8A-8C.

Scaffolds were assessed qualitatively for moldability by wetting them with physiologic saline and hand kneading for one to two minutes. Scaffolds were qualitatively assessed to see if they resisted hand-molding and if so, to what extent; whether they could be torn apart by hand, and after molding if they remained cohesive; e.g., did the polymer matrix remain intact and retain a large fraction of the calcium phosphate.

The scaffolds of Examples 1-1 and 1-2 could be torn apart by hand, were relatively stiff and only slightly moldable, however the scaffolds remained intact and retained most if not all of the calcium phosphate. The scaffold of Example 1-3 could be torn apart by hand, were absorbent and partially moldable, their polymer matrix remained intact but lost some calcium phosphate during hand-kneading. The scaffold of Comparative Example 1-1 could be torn apart by hand, however, the polymer matrix did not remain intact upon de-molding and lost calcium phosphate easily upon de-molding.

Experimental Example 2: Scaffold Quality as a Function of Amount of Polymer Solution

Experimental Example 2 studies scaffold quality as a function of amount of polymer solution. Examples 2-1 through 2-3, the results of which are depicted in FIGS. 9A-9C, were made using the same methods, except different amounts of polymer solution were used in each Example. Comparative Examples 2-1 through 2-3, the results of which are depicted in FIGS. 9D-9F, were made using the same methods, except using a polymer concentration lower than that of Examples 2-1 through 2-3. Examples 2-1 through 2-3 and Comparative Examples 2-1 through 2-3 were performed using PCL filament-derived material as used in Experimental Example 1.

Example 2-1: 14 g Polymer Solution

A scaffold of Example 2-1 was prepared in the same manner as that of Example 1-2, using a 10 wt % PCL-GAA solution, except using 14 g of 10 wt % PCL-GAA solution. The resulting scaffold is depicted in FIG. 9A.

Example 2-2: 12 g Polymer Solution

A scaffold of Example 2-2 was prepared in the same manner as that of Example 1-2. The resulting scaffold is depicted in FIG. 9B.

Example 2-3: 10 g Polymer Solution

A scaffold of Example 2-3 was prepared in the same manner as that of Example 1-2, using a 10 wt % PCL-GAA solution, except using 10 g of the 10 wt % PCL-GAA solution. The resulting scaffold is depicted in FIG. 9C.

Comparative Example 2-1: 8 g Polymer Solution

A scaffold of Comparative Example 2-1 was prepared in the same manner as that of Example 1-2, using a 10 wt % PCL-GAA solution, except using 8 g of the 10 wt % PCL-GAA solution. The resulting scaffold is depicted in FIG. 9D.

Comparative Example 2-2: 6 g Polymer Solution

A scaffold of Comparative Example 2-2 was prepared in the same manner as that of Example 1-2, using a 10 wt % PCL-GAA solution, except using 6 g of the 10 wt % PCL-GAA solution. The resulting scaffold is depicted in FIG. 9E.

Comparative Example 2-3: 4 g Polymer Solution

A scaffold of Comparative Example 2-3 was prepared in the same manner as that of Example 1-2, using a 10 wt % PCL-GAA solution, except using 4 g of the 10 wt % PCL-GAA solution. The resulting scaffold is depicted in FIG. 9F.

The scaffolds of Examples 2-1 through 2-3, having about 10 g or greater of 10 wt % PCL-GAA solution, exhibited robust and cohesive properties as shown in FIG. 9A-9C. However, the scaffolds of Comparative Examples 2-1 through 2-3, having about 8 g or less of 10 wt % PCL-GAA solution, were less robust and cohesive, and exhibited loss of at least calcium phosphate upon de-molding. In some cases, such as Comparative Example 2-3, the scaffold additionally exhibited a loss of structure upon de-molding as shown in FIG. 9F.

Experimental Example 3: Scaffolds Using Other Polymers and Solvents

Experimental Example 3 studies biodegradable or non-biodegradable polymers, other than those polymers used in Experimental Examples 1 and 2, which may be used to create scaffolds.

Example 3-1: Poly(D,L-lactic-co-glycolide) in Acetone

A scaffold of Example 3-1 was made from a polymer solution where about 1.7 g of poly (DL-lactic-co-glycolide) (50:50) (Available from Sigma Aldrich Chemicals) was dispersed in about 12 g Acetone. The polymer solution was added to a mold which included about 3.4 g of calcium phosphate (Vitoss® micromorsels, available from Stryker Orthobiologics). The scaffold was prepared using water as a precipitating agent as described in Experimental Example 1. The scaffold of Example 3-1 exhibited poor integrity as shown in FIG. 10. It is possible that increasing the concentration of polymer in the polymer solution, similar to results obtained in Experimental Example 1, may yield a scaffold having more desirable properties.

Experimental Example 4: Scaffold Including a Substrate

Scaffolds were prepared using various substrates, such as screens, porous polymer implants, three dimensional substrates, and bone suture anchors.

Example 4-1: Scaffold Including a Screen

A paste was made from a mixture of a polymer solution (10 wt % PCL-GAA) and calcium phosphate (Vitoss® subfine, further sieved to obtain about 250 μm average particle size) in a weight ratio of about 1.0:1.5-2.0. Using a metal spatula, the paste was smeared on both sides of a stainless steel metal screen to cover about one half the surface area of the screen (316 Stainless, 50-100 mesh), and then immersed in water for about 15 to 30 seconds to precipitate the PCL leaving a PCL-calcium phosphate layer adhered to, and covering both sides of the metal screen as shown in FIG. 11.

Example 4-2: Scaffold Including Porous Polymer Implants

As shown in FIG. 12A-12D, scaffolds can be formed using porous high density polyethylene (HDPE) sheets as substrates (FIGS. 12A-12C) or HDPE cranial implants (MedPor, FIG. 12D).

The scaffolds show in FIGS. 12A, 12B, and 12D were made using PCL as a polymer and calcium phosphate (Vitoss® particles, about 250 μm). In the scaffold depicted in FIG. 12C, bioactive glass was substituted in place of calcium phosphate. The scaffolds of FIGS. 12A-12D were manufactured by one of three methods: (1) immersing the materials in a coating solution including 10% PCL-GAA and one of calcium phosphate or bioactive glass, (2) depositing the coating solution onto the substrates, for example, using a brush or another deposition device, or (3) immersing the substrates in a 10% PCL-GAA solution, and then dipping the wetted substrates in one of calcium phosphate or bioactive glass. In each method, the coated substrates were then submerged under water for about 15 to about 30 seconds to precipitate the polymer to form the scaffold.

In FIG. 12A, a porous HDPE sheet was dipped in a 10 wt % PCL-GAA solution including calcium phosphate at the bottom edge, and then precipitated, resulting in a small, uneven area coated a scaffold. In FIG. 12B, a porous HDPE sheet was immersed in 10% PCL-GAA, and then the surface of the porous HDPE sheet was pressed against a dry bed of calcium phosphate particles. It was then immersed in water to precipitate the scaffold, resulting in the entire surface coated with, and white from, calcium phosphate. In FIG. 12C, a porous HDPE sheet was coated similar to that of the sheet in FIG. 12B, except bioglass (Combeite, 90-150 microns) was used instead of calcium phosphate. The sheet shown in FIG. 12C is completely coated with a PCL-bioglass scaffold but is not bright white like a scaffold made of PCL and calcium phosphate since the bioglass is clear to moderately cloudy but translucent, and not an opaque white.

Example 4-3: Scaffold Including Three-Dimensional Substrate

Example 4-3 uses a polylactic acid (PLA) wedge as a substrate as shown in FIG. 13A. The PLA has been 3D printed, and has a cage configuration with a slotted base. A 10% PCL-GAA calcium phosphate (Vitoss® micromorsel suspension) was prepared in the same manner as described in Example 4-1, and packed into the interstices of the PLA wedge. The packed PLA wedge was submerged in a water bath for about 15 to about 30 sec, and then air dried. The resulting scaffold comprised a stiff cage of PLA in which a matrix of PCL embedded with calcium phosphate was stably incorporated throughout as shown in FIG. 13B.

Example 4-4: Scaffold Including Bone Suture Anchors

As shown in FIG. 14A, a scaffold can include a bone suture anchor as a substrate. For example, one exemplary bone suture anchor is ICONIX™ bone suture anchors, available from Stryker, Inc.

The scaffolds of Example 4-4 are prepared using a PCL-GAA-calcium phosphate mixture or a PCL-GAA-bioactive glass mixture, each used in same proportions as for other pastes described in Example 4-1, were used to coat ICONIX bone suture anchors. The bone suture anchors are then dipped into the mixtures to coat the anchors with the mixture. The coated anchors are then submerged in a water bath for about 15 to about 30 seconds to precipitate the polymer to form the scaffold, and then air dried.

As shown in FIGS. 14B-14D, a PCL-calcium phosphate (FIGS. 14B, 14D or PCL-bioactive glass scaffold (FIG. 14C) including a bone suture anchor as a substrate can be formed. At low magnification (FIGS. 14B-14D), the scaffolds appeared as thick white to white-gray coatings on the bone suture anchor. As shown in FIG. 14D, the scaffolds have sufficient flexibility to be ‘bunched’, i.e., the bone suture anchor is subjected to a manipulation that results in it having a different configuration. At high magnification (FIG. 15), scaffolds having bone suture anchors coated with PCL-calcium phosphate exhibited a surface with a jagged profile. The jagged profile may be caused by the calcium phosphate, which can have a particulate form.

At low magnification (FIG. 14C, FIG. 16A) bioactive glass particles in scaffolds having bone suture anchors coated with PCL-bioactive glass were too small to resolve. However, Energy-dispersive X-ray spectroscopy (EDAX) analysis (FIG. 16B, EDAX silicon map of FIG. 16A; FIG. 16C) of the PCL-bioactive glass scaffolds show elements consistent with both PCL (carbon and oxygen) and bioglass (calcium and silicon).

Experimental Example 5: Fine Structure and Atomic Composition of Scaffold

Experimental Example 5 examines fine structure and atomic composition of scaffolds made with and without calcium phosphate by scanning electron microscopy (SEM) and EDAX, respectively.

Example 5-1: PCL Scaffold

Example 5-1 is made in the same manner as Example 1-3, except calcium phosphate is omitted. The scaffold of Example 5-1 had a sheet-like, porous appearance overall (FIG. 17A), in some areas appearing to be comprised of multiple layers, with some fibrous or fiber-like structures (FIG. 17B) that were of irregular diameters. Varying numbers of large and small pores were also evident in many areas of the scaffold surface (FIGS. 17A, 17B). There was no evidence of a nano-fibrillar PCL composition as is characteristic of scaffolds fabricated by electrospinning of solubilized PCL.

EDAX analysis (FIG. 18) of a region of the scaffold shown in FIG. 17A showed that the majority of the scaffold was comprised of carbon and oxygen, which was as expected for a scaffold made from a PCL solution. Some salts were present in small quantities, which is attributed to reagents used to make the scaffold. The presence of gold is due to sputter-coating the scaffold with gold during SEM sample preparation.

Example 5-2: PCL-Calcium Phosphate Scaffold

Example 5-2 is made in the same manner as Example 1-3. The scaffold of Example 5-2 showed similar scaffold morphology to that of Example 5-1, except for the presence of calcium phosphate particles (Vitoss® micromorsels) were evident throughout as shown in FIG. 19. In addition, amorphous and ordered crystals appeared to be associated with both PCL and calcium phosphate.

EDAX analysis (FIGS. 20A, 20B) of regions of the scaffold depicted in FIG. 19 indicated the crystals comprised calcium phosphate. It is speculated that the crystals may arise from acid solubilization (in GAA) of at least part of the calcium phosphate and then recrystallization of the calcium phosphate on the PCL. Calcium phosphate crystal deposition on the surface of the scaffold may be minimized if desired. For example, after precipitation of PCL, a copious water rinse and/or base neutralization of GAA could be performed, optionally followed by rapid drying.

Experimental Example 6: Scaffold Thickness as a Function of Amount of Precipitating Agent

Experimental Example 6 studies scaffold dimensions and quality as a function of an amount of precipitating agent. Examples 6-1 through 6-5, the results of which are depicted in FIGS. 21A and 21B were made using the same methods, except different amounts of precipitating agent were used in each Example. Comparative Example 6-1, the result of which is depicted in FIG. 21B, was made using the same methods, except omitting a precipitating agent. Scaffolds in Experimental Example 6 did not include a calcium phosphate and/or bioactive additive, such as Vitoss® micromorsels.

Example 6-1: Scaffold Prepared from 10% PCL-GAA Solution Using 1 g Water

A 10% PCL-GAA solution was prepared by the same methods as described in Example 1-2. About 2 g of the 10% PCL-GAA solution were added to a 25 ml borosilicate glass beaker (Kimax®, available from Kimble). About 1 g of water was added dropwise to the surface of the 10% PCL-GAA solution. The water was added over a period of less than one minute. The mixture was allowed to incubate for about 15 to about 30 minutes at room temperature and ambient pressure conditions. After the incubation period the scaffold was dried at room temperature and atmospheric conditions for about 2 to 3 days and removed from the beaker. The scaffold is depicted in FIG. 21A and the thickness of the scaffold is depicted in comparison to Examples 6-2 through 6 and Comparative Example 6-1 in FIG. 21B.

Examples 6-2 Through 6-5: Scaffold Prepared from 10% PCL-GAA Solution Using 2 g, 4 g, 6 g, and 10 g Water

Examples 6-2 through 6-5 are made using the same procedure described for Example 6-1, except about 2 g, about 4 g, about 6 g, and about 10 g of water, respectively, were added dropwise to the 10 wt % PCL-GAA solution. The resulting scaffolds and thickness comparisons are depicted in FIGS. 21A, 21B.

Comparative Example 6-1: Scaffold Prepared from 10% PCL-GAA Solution and Air Drying

Comparative Example 6-1 is made using the same procedure described for Example 6-1, except water was omitted. The resulting scaffold and thickness comparison to the other Examples is depicted in FIGS. 21A, 21B.

As shown in FIG. 21A, the scaffolds of Examples 6-2 through 6-5 have a bright white, styrofoam-like appearance, and are porous. The scaffolds expand in height relative to the amount of water added up to about 6 g (Example 6-4). At higher amounts of water (8 g, not shown) or 10 g (Example 6-5) the scaffolds continue to expand to greater heights but their shapes become irregular. In contrast, Comparative Example 6-1, where water was not added, formed a thin, slightly flexible by manual manipulation, wrinkled disk with little or no apparent porosity.

Comparative Example 7: Scaffold Prepared Using a Different Order of Process Steps

Comparative Example 7 is made using the same procedure described for Example 6-4, except about 6 g of water was added to the borosilicate beaker, and 2 g of 10% PCL-GAA solution was added dropwise to the water. The resulting scaffold is depicted in FIG. 22 in comparison to the scaffold of Example 6-4. The scaffold of Comparative Example 6-2 is mushroom-shaped and has a non-homogenous density throughout the scaffold. The scaffold is also denser than that of Example 6-4.

Experimental Example 8: Scaffold Quality as a Function of Molecular Weight

Experimental Example 8 studies scaffold quality as a function of molecular weight of PCL. Examples 7-1 and Comparative Examples 8-1 and 8-2 were made using the same methods, except different molecular weights for each polymer.

Example 8-1: Scaffold Prepared from 10% PCL-GAA Solution Using Mn=80,000 g/mol PCL

The scaffold of Example 7-1 was prepared by the same procedure as Example 1-2, except PCL pellets (Sigma-Aldrich Chemicals, Lot No. MKBV3325V) having Mn=80,000 g/mol were used in place of PCL filaments.

Comparative Example 8-1: Scaffold Prepared from 10% PCL-GAA Solution Using Mn=45,000 g/mol PCL

The scaffold of Comparative Example 7-1 was prepared by the same procedure as Example 1-2, except PCL pellets (Sigma-Aldrich Chemicals, Lot No. MKBT6624V) having Mn=45,000 g/mol were used in place of PCL filaments.

Comparative Example 8-2: Scaffold Prepared from 10% PCL-GAA Solution Using Mn=14,000 g/Mol PCL

The scaffold of Comparative Example 7-2 was prepared by the same procedure as Example 1-2, except PCL pellets (Sigma-Aldrich Chemicals, Lot No. MKBR890V) having Mn=14,000 g/mol were used in place of PCL filaments.

Upon removing the scaffold of Example 7-1 from the mold, the scaffold was intact and robust. In contrast, the scaffold of Comparative Example 7-1 was partially intact and insufficiently robust. The scaffold of Comparative Example 7-2 was not robust and fell apart upon removal from the mold.

It is to be understood that the disclosure set forth herein includes all possible combinations of the particular features set forth above, whether specifically disclosed herein or not. For example, where a particular feature is disclosed in the context of a particular aspect, arrangement, configuration, or embodiment, that feature can also be used, to the extent possible, in combination with and/or in the context of other particular aspects, arrangements, configurations, and embodiments of the invention, and in the invention generally.

Furthermore, although the invention herein has been described with reference to particular features, it is to be understood that these features are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications, including changes in the sizes of the various features described herein, may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention. In this regard, the present invention encompasses numerous additional features in addition to those specific features set forth in the claims below. Moreover, the foregoing disclosure should be taken by way of illustration rather than by way of limitation as the present invention is defined by the claims set forth below. 

The invention claimed is:
 1. A method of forming a bioactive filamentary structure, comprising the steps of: applying a polymer solution around a filamentary structure; after the polymer solution applying step, applying synthetic bone graft particles to the polymer solution and around the filamentary structure; and after the synthetic bone graft particles applying step, precipitating a polymer from the polymer solution such that the synthetic bone graft particles and the polymer coat the filamentary structure, wherein the polymer is precipitated from the polymer solution by applying a precipitating agent to the polymer solution, and wherein, after the polymer precipitating step, the bone graft particles are embedded in the polymer.
 2. The method of claim 1, wherein the synthetic bone graft particles are applied around the filamentary structure by placing the coated filamentary structure into a container of synthetic bone graft particles and then removing the filamentary structure from the container.
 3. The method of claim 2, wherein the container of the synthetic bone graft particles is shaken during placement of the coated filamentary structure into the container.
 4. The method of claim 1, wherein the synthetic bone graft particles include either one or both of calcium phosphate and a bioactive additive.
 5. The method of claim 1, wherein the polymer solution includes at least one solvent selected from the group consisting of glacial acetic acid (GAA), acetic acid, anisole, chloroform, methylene chloride, acetylchloride, 2,2,2 trifluoroethanol, trifluoroacetic acid, 1,2-Dochloroethane, and mixtures thereof.
 6. The method of claim 5, wherein the polymer solution comprises polycaprolactone (PCL) and glacial acetic acid (GAA).
 7. The method of claim 1, wherein the precipitating agent is selected from the group consisting of sodium phosphate buffer, water, ethanol, 1-propanol, isopropyl ether, 2-butanol, hexane, and mixtures thereof.
 8. The method of claim 1, wherein the polymer solution is applied around the filamentary structure by spraying the polymer solution around the filamentary structure.
 9. The method of claim 1, wherein the step of precipitating the polymer from the polymer solution includes immersing the polymer solution in the precipitating agent after applying both the synthetic bone graft particles and the polymer solution around the filamentary structure.
 10. The method of claim 1, wherein the step of applying a precipitating agent to the polymer solution comprises the step of applying a first buffer to the polymer solution after the polymer solution is applied around the filamentary structure to at least partially neutralize the polymer solution.
 11. The method of claim 10, wherein the step of applying a precipitating agent to the polymer solution further comprises the step of applying a second buffer to the polymer solution after the first buffer is applied around the filamentary structure to further dilute the polymer solution.
 12. The method of claim 10, further comprising the step of drying the coated filamentary structure at least after the first buffer is applied to the polymer solution.
 13. The method of claim 12, further comprising the step of packaging the dried coated filamentary structure disposed on an inserter.
 14. The method of claim 1, further comprising covering a portion of the filamentary structure such that the bone graft particles do not coat the covered portion of the filamentary structure during the synthetic bone graft particles applying step.
 15. The method of claim 14, wherein the covering step includes applying a mask over openings defined by the filamentary structure.
 16. The method of claim 15, wherein the mask is a tape or a film.
 17. The method of claim 1, wherein the bone graft particles are wedged between fibers of the filamentary structure after the synthetic bone graft particles applying step.
 18. The method of claim 1, wherein the bone graft particles are 150 μm or less in size.
 19. The method of claim 1, wherein the bone graft particles are 90 μm or less in size.
 20. The method of claim 1, wherein the bone graft particles are embedded in the polymer such that at least a portion of the bone graft particles are exposed through the polymer that coats the filamentary structure after the polymer precipitating step. 